JPH08115874A - Adjusting method for position deviation measuring optical system and position deviation measuring apparatus - Google Patents

Abstract

PURPOSE: To obtain a deviation value near the original deviation of an optical system, without being influenced by its distortion, by rotating the same position deviation measuring pattern by 180 deg. and taking a half of the difference from the deviation before rotating. CONSTITUTION: MPU 19 executes a deviation measuring program 21a about a mark pattern, thereby measuring the deviation Δa of a registration pattern on a wafer 9. The wafer 9 is rotated by 180 deg. to measure the deviation Δr of this pattern. The true mark deviation δ is computed according to δ=(Δa-Δr)/2. A linear shifter 13 is controlled to move the detection center of a detector by a field of view corresponding to the deviation δ whereby this detection center can be aligned with the original center of an optical system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a measuring optical system of a positional deviation amount measuring apparatus for measuring a positional deviation amount between various patterns formed on a wafer, so-called registration, and a positional deviation amount. Regarding the measuring device, in detail, in a certain semiconductor manufacturing process, the amount of misalignment between the resist pattern formed by exposure through a mask or the like and the etched pattern already formed in the preceding process is increased. The present invention relates to a method of adjusting a measurement optical system of a positional deviation amount measuring device that enables accurate measurement.

[0002]

2. Description of the Related Art In the manufacture of semiconductor ICs, various patterns are formed on a substrate wafer having a smooth surface. Since it is necessary that the positions of these patterns be accurately formed, the amount of positional deviation between the already formed pattern and the pattern to be formed next, that is, registration, is precisely measured. Has been done. In response to the dramatic increase in the storage capacity of DRAMs from 16M to 64M and 256M, the measurement and inspection of this amount of positional deviation are becoming more and more important.

In order to manufacture a DRAM having a high-density storage capacity, the detection optical system of the exposure apparatus is adjusted, and the center of the detection optical system and the center of each chip on the wafer are positioned with high precision. is important. In the conventional positioning, the center of the wafer surface is aligned with the center of the objective lens of the optical system of the exposure apparatus, the relay lens, and the center of the detector such as CCD for detecting the alignment mark by the laser light. It is aligned.

[0004]

However, when the storage capacity of the DRAM becomes 16 M or more, the line width as a pattern becomes 0.7 μm or less, so that the allowable error in registration becomes 15 nm or less. There is a problem that the required accuracy cannot be achieved due to the distortion error of the optical system only by adjusting the optical system. An object of the present invention is to solve such a problem of the conventional technique, and to provide a position deviation amount measuring optical system adjusting method and a position deviation amount measuring device capable of measuring a position deviation amount with high accuracy. To provide.

[0005]

The feature of the adjusting method of the position shift amount measuring optical system of the present invention is that the center is positioned at the center of the visual field and the light from the position shift amount measuring pattern is received to determine the position shift amount. Having a detector for generating a detection signal representative of,
In the method of adjusting the measurement optical system in the positional deviation amount measuring device that measures the positional deviation amount by the detection signal, the measuring device includes a moving mechanism that moves the detection center of the detector, and measures the deviation amount of the positional deviation amount measurement pattern. The obtained displacement amount is defined as a first displacement amount, the displacement amount measurement pattern is rotated by 180 ° and the displacement amount is measured, and the displacement amount is determined as a second displacement amount. The difference from the deviation amount of 2, for example, 1/2 of this difference is obtained as the third deviation amount, and the center of the detector is made to correspond to the third deviation amount by the moving mechanism according to the third deviation amount. It is moved by the amount of the field of view. Also,
The position shift amount measuring device of the present invention controls the moving mechanism according to the third shift amount to automatically move the center of the detector by the field of view corresponding to the third shift amount. .

[0006]

In this way, the same positional deviation amount measurement pattern is
The amount of deviation is measured by rotating it by 80 °, and by taking the difference from the deviation before rotation, especially 1/2 of the difference, a value close to the original deviation without being affected by the distortion of the optical system is set to the third value. It can be obtained as a deviation amount. The principle will be described later.
Therefore, the detection center of the detector can be made to coincide with the original center of the optical system by moving the detection center of the detector by the visual field corresponding to the third shift amount. As a result, there are almost no measurement errors due to distortion of the optical system,
Highly accurate shift amount can be measured.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of a registration measuring apparatus according to an embodiment to which the method for adjusting a positional deviation amount measuring optical system of the present invention is applied, and FIG. 2 shows a center of an optical system and a center of a detector. A flow chart of the position adjustment processing, FIG. 3 is an explanatory diagram of the relationship between the distortion amount and the displacement amount of the registration pattern, FIG. 4 is an explanatory diagram of measuring the displacement amount by shifting the measurement point from the center of the visual field, and FIG. FIG. 6 is an explanatory diagram of an example of the measurement result in FIG. 4, FIG. 6 is an explanatory diagram of a registration pattern, and FIG. 7 is an explanatory diagram of an arrangement of chips and registration patterns on a wafer and a detection signal of a detector. .

FIG. 6A shows an example of a registration pattern (mark pattern) 30 having a resist pattern 30 inside the etching pattern, and FIG. 6B shows a registration pattern 30 having a resist pattern above the etching pattern. 3C is an example of the registration pattern 30 having an etching pattern inside the resist pattern. The upper side shows the plan view, and the lower side shows the sectional view. These are composed of an etching pattern 31 which is a part of the pattern already formed in the previous step and a resist pattern 32 for the pattern to be formed, and they have mutually square shapes, and one of them is arranged inside. It like this
Registration patterns 30 of (a), (b), and (c)
As shown in FIG. 7A, one of them is a registration pattern (mark pattern) 30 at four positions symmetrically with respect to the center of a certain chip 24 (arbitrary chip) on the wafer.
a, 30b, 30c and 30d, respectively. These four registration patterns are provided around the periphery of each of the chips. FIG. 7B shows a detection signal in the X-axis direction (hereinafter, X-axis detection signal) of the registration pattern 30a detected by the CCD detector in the focused state, for example, the one of FIG. 6B. The detection signal in the Y-axis direction has a similar waveform, but is omitted in the figure.

The peak positions a and d of the X-axis detection signal are detected, their center XE and peak positions b and c are detected, and the difference ΔX between these centers XR is the amount of deviation in the X direction. If the amount of deviation is within the allowable range, the resist pattern 32
The positions are matched, and the next pattern is formed by using the resist having the resist pattern 32 as a part as a mask. The above is also performed in the Y-axis direction. In either one of the axis directions, if either ΔX or ΔY is out of the allowable range, the wafer and the mask are removed after removing the resist. And are offset by the amount of deviation and aligned again, and then the same resist pattern is formed again by exposure.

By the way, the detectors that receive the optical reflected light in order to detect such a shift amount are the CCD linear sensor 10 in the X-axis direction and the CCD linear sensor 11 in the Y-axis direction in FIG. On the other hand, as in the conventional case, the center of the objective lens 1 and the relay lenses 2a and 3 are aligned with the laser beam.
a, and when the centers of the detectors of the CCDs 10 and 11 are adjusted, the objective lens system 1, the relay lens 2a, the cylindrical lens 2b (X-axis direction), the relay lens 3a,
There is a deviation between the center of the visual field determined by the optical system such as the cylindrical lens 3b (Y-axis direction) and the center of the actual optical system. This deviation occurs due to the accuracy of the outer diameter of the lens, the processing accuracy, the mounting state, and the adjustment state of the optical system. of course,
Here, it is assumed that the center of the visual field by this optical system and the centers of the CCD linear sensors 10 and 11 which are the detectors have been adjusted and coincide with each other.

Reference numeral 4 denotes a half mirror, which is in the X direction and the Y direction.
The reflected light from the wafer is separated into the direction and the detection system. 5
Is an illumination optical system, which includes a light source 50, a light amount adjustment filter 51, a fiber 52 provided in the middle of the optical path,
It includes a diaphragm mechanism 53 for narrowing the illumination light, a field diaphragm 54, a half mirror 55, and a lens system provided corresponding to each of these elements for generating condensed light or parallel light. In addition, 6a and 6b are X-direction and Y-direction visual field setting variable slits provided in front of the relay lenses 2a and 3a, respectively, 7 is a wafer chuck, and 8 is a wafer chuck 7 which is moved in XYZ directions. XYZ moving stage, 9
Is a wafer chucked by the wafer chuck 7.

As shown in FIG. 3, the distortion of the optical system generally increases from the center of the optical system to a quadratic curve. Normal,
With conventional adjustment alone, the center of the optical system (hereinafter referred to as the center of distortion for distinguishing from the center of the visual field) is displaced from the visual field center Os. If the amount of deviation between the center Od of the distortion and the center Os of the field of view becomes large, highly accurate registration measurement cannot be performed no matter how highly accurate adjustment is made. This is because the registration measurement is performed at a position where the distortion becomes large as the center Od of the distortion deviates from the center Os of the visual field. On the other hand, if the center Od of the distortion is made to coincide with the center of the detection system of the CCD linear sensors 10 and 11, the center of the detection system and the center of the optical system coincide with each other even in the conventional adjustment, the distortion is small, and high precision is achieved. You can measure.

Therefore, in FIG. 1, linear moving mechanisms 12 and 13 for moving the positions of the CCD linear sensors 10 and 11 in the X and Y directions are provided. Control device 2
0 determines the position of the distortion center Od of the optical system and controls the moving mechanisms 12 and 13 and the driving circuit 14 for moving the moving mechanism so that the centers of the CCD linear sensors 10 and 11 coincide with the center of distortion. To do. A / D conversion circuit (A / D) 15
Is digitized by the control device 20 under the control of the CCD linear sensors 10 and 11 and sent to the control device 20.

The control unit 20 is composed of an image memory 16, a digital signal processor (DSP) 17, a focus controller 18, an MPU 19, a memory 21, etc., and the MPU 19 and DSP 17, the focus controller 18, the memory 21, etc. via a bus 22. Are connected to each other. A / D 15 is a CCD linear sensor 10, 1
A detection signal from 1 is received and A
The D / D converted data is sent to the image memory 16. The image memory 16 sequentially stores the data from the A / D 15.

The DSP 17 receives the digital data of the image memory 16 under the control of the MPU 19 and then receives the digital data shown in FIG.
The deviation amount ΔX (ΔY) shown in (b) is calculated at high speed, and the calculation result is sent to the MPU 19. This is a processor dedicated to calculating the amount of deviation. The focus controller 18 is controlled by the MPU 19 to control the CCD linear sensor 1
0, 11, A / D 15, image memory 16 are controlled, and data from the image memory 16 is received to move the XYZ moving stage 8
Is moved in the Z direction for focusing. It should be noted that this focusing process is omitted because it is not directly related to the invention. The memory 21 is provided with a mark deviation amount measurement program 21a, a deviation amount calculation program 21b with respect to the distortion center Od, a visual field center deviation deviation amount calculation program 21c, a CCD center alignment program 21d, and the like. Reference numeral 23 denotes a stage drive circuit that sends a drive signal for moving the XYZ moving stage 8 in the X, Y, Z directions to the XYZ moving stage 8 according to a control signal from the control device 20.

The alignment process of the strain center Od and the center of the detector will be described below with reference to FIG. 2 centering on the X-axis direction. Since the same applies to the Y-axis direction, description thereof will be omitted except when particularly necessary. First, MPU1
9 executes a mark pattern deviation amount measuring program 21a to execute a registration pattern (as a mark pattern) on the wafer 9, for example, inside the outer pattern of the registration pattern 30a as shown in FIG. 3 (a). At the center of the frame 33, the field center Os of the objective lens system 1
Is positioned, the DSP 17 is activated, and the deviation amount Δa of the registration pattern 30a is measured (step 10).
0).

Next, as shown in FIG. 3B, the wafer 9 is rotated by 180 °, and the chip 24 before being rotated with respect to the center O on the wafer 9 with respect to the registration pattern 30a before being rotated. Similarly, the visual field center Os of the objective lens system 1 is positioned at the center of the outer inner frame 33 with respect to the registration pattern 30a around the rotated chip 24 shown by the dotted line in a position symmetrical with respect to Start up and shift amount Δr of registration pattern 30a
Is measured (step 101). Then, the true mark deviation amount δ is calculated by δ = (Δa−Δr) / 2. That is, δx = (Δax−Δrx)
/ 2, δy = (Δay-Δry) / 2, then δx, δy
Is calculated (step 102). Here, when the distortion amount from the optical system center at the visual field center Os of the registration pattern 30a is Da, the distortion amount Dr of the optical system at the visual field center Os of the registration pattern 30a rotated by 180 ° is also Dr≈Da.

The graphs shown on the lower side of FIGS. 3 (a) and 3 (b) are for explaining the state of this distortion. FIG. 3 (a) shows the distortion center in the visual field at 0 ° before rotation. The relationship between Od and the deviation amount vector V is shown. In this case, the distortion amount D added to the deviation amount Δ is Da, which is the difference between Od and Os. On the other hand, (b) shows the relationship between the strain center Od and the displacement amount vector V in the visual field after 180 ° rotation. In this case, the strain amount added to the displacement amount Δ is Od and Os.
And the difference is Dr. At 0 ° and 180 °, the directions of the vector V are reversed and their lengths are almost equal. The strain amount from the strain center Od increases radially, and the strain amounts Da and Dr act in the opposite directions to the shift amounts Δa and Δr. Moreover, the directions of the deviation amounts Δa and Δr are also reversed. Therefore, the lengths of the strains that affect the shift amount are in the same direction. That is, if the strain acts on the strain amount Da in the direction of shortening its length, the strain direction Dr acts on the strain amount Dr in the direction of its length being reversed and extended. Therefore, in both cases, the effect of the length due to the distortion is in one direction of the subtraction direction or the addition direction.

Further, in FIG. 3, the curvature of the quadratic curve is drawn large for the sake of convenience of explanation, but the distance r from the distortion center Od to the visual field center Os is usually not so large that the visual field center is not. If the curves before and after Os are treated as straight lines with a certain inclination, the values of the strain amounts Da and Dr applied to the vector V become substantially equal. That is, for the deviation amounts Δa and Δr, Δa = Da + δ Δr = Dr−δ where Da≈Dr As a result, (Δa−Δr) / 2 = {(Da + δ) − (Dr−δ)}
/ 2≈δ. Although FIG. 3 shows an example in which the center O of the inner pattern and the visual field center Os are on the same right side with respect to the distortion center Od at the registration pattern 30a positions of 0 ° and 180 °, respectively. Even if they are on the same left side, the relations in which the strain amounts Da and Dr act in opposite directions on the shift amounts Δa and Δr do not change.

On the other hand, when the distortion center Od and the visual field center Os are close to each other and the positions of the registration pattern 30a are 0 ° and 180 °, the center O of the inner pattern and the visual field center Os are relative to the strain center Od. And the distortion amounts Da and Dr are on the opposite sides, the deviation amounts Δa and Δr
The amount that acts in the opposite direction to each other becomes unbalanced. The distortion amount of one of them becomes larger than that of the other,
The distortion amount at this time is a relationship in which the deviation amounts Δa and Δr are measured with respect to the length within a predetermined allowable range.
Since the strain amounts Da and Dr with respect to r are small, the influence on the true shift amount δ is small as compared with the above case. As a special case, when the distortion center Od and the visual field center Os are close to each other, the distortion amounts Da and Dr become the deviation amounts Δa and Δr.
, But they act in the same direction as each other, but in such a case, Δa≈Δr, and therefore the center position of the detector does not have to be corrected.

That is, when other than Δa≈Δr, in other words, whether Δa−Δr> α or not is determined by δx> αx or δy.
It is determined whether it is> αy (step 103). If both are small, it is determined that the NO condition is satisfied and the distortion center Od and the visual field center Os are not displaced, and no adjustment is performed. When either one of the conditions is satisfied, YES is obtained and δx = (Δax−Δrx) / 2, δy = (Δay
The calculated true mark deviation amount δx in the X-axis direction and the true mark deviation amount δy in the Y-axis direction are stored in a predetermined area of the memory 21 according to −Δry) / 2 (step 104). The above α (= αx, αy) can be obtained as an experimental value. Next, the registration pattern 30
Rotate a by 180 ° and return it to its original position (step 10
5) The MPU 9 executes the visual field center deviation shift amount calculation program 21c, fixes the visual field center Os, moves the registration pattern 30a on the X axis, and measures the deviation amount Δa at each position. Similarly, the amount of deviation is measured in the Y-axis direction (step 106).

FIG. 4 illustrates the measurement state of this deviation amount Δa. The registration pattern 30a
,,, are moved in this order, and the deviation amount Δa is measured at each position. During this time, the visual field center Os is fixed at the position where Δa was first measured. Therefore, the measurement value at is not necessary, but is shown for convenience of explanation. As a result, it is possible to measure the shift amount Δ corresponding to the shift amount of the center of the inner frame 33 from the visual field center Os. FIG. 5 shows an example of the result. The true mark deviation amount δ
If x = -39 nm, then in the graph of FIG. 4 (b),
It can be seen that that point is located at +4.4 μm with respect to the fixed visual field center Os. Therefore, this position is set as a movement control amount for the CCD, and Xo = + 4.4 μm is stored in a predetermined area of the memory 21. Similarly, the movement control amount Yo is calculated in the Y direction and stored in the memory 21.

By the way, in FIG. 5, the shift amount Δa is X.
The decrease along with the increase in the axial direction is that the strain amount direction is reversed to the left and right with respect to the length measurement direction with the strain center Od as a boundary in the visual field, so that the strain amount is changed from the measurement amount Δ to the strain amount D. Will be drawn. Here, the strain center O
Since the amount of distortion at d is not measurable, it is considered that the amount of distortion is very small, and the position corresponding to the true mark deviation amount δx is set as the position of the distortion center Od. Therefore, in step 107, Δax =
It is determined whether δx, Δay = δy. If they do not match, the registration pattern is moved by a predetermined amount in the axial direction, and the process returns to step 106. Detecting the coincidence point in this way is an ideal case, and assuming that there is no distortion amount at the center of distortion, the displacement amount measured at this coincidence point corresponds to the true displacement amount. is there. That is, the registration pattern 30a is ...
, The order is moved and the amount of deviation Δ at each position
ax (= value of Δa on the X-axis) is δx, deviation amount Δay (=
The value of Δa on the Y-axis) is the value that matches or is the closest to δy. The X coordinate movement control amount Xo and the Y coordinate movement control amount Y.
o is obtained (steps 106, 107, 108). Then, Xo and Yo are stored in a predetermined area of the memory 21 (step 109).

Next, the MPU 9 executes the CCD center alignment program 21d, reads the movement control amounts Xo and Yo from the memory 21, and sends a control signal for moving the light reception center of the CCD 10 in the visual field by the coordinates Xo and Yo. It is generated according to the magnification of the field of view and the light-receiving area and is sent to the drive circuit 14 for moving mechanism or the like.
2 by controlling X in the visual field of the light receiving center of CCD 10.
The CCD 11 is controlled by controlling the linear movement mechanism 13 in the Y direction by a control signal for moving by o and moving by the field of view Yo.
The light receiving center of is moved by Yo in the visual field so that the detection center coincides with the distortion center Od or is positioned in the vicinity thereof (step 110).

[0025]

As described above, in the registration measuring method and apparatus according to the present invention,
By rotating the same position displacement amount measurement pattern 180 ° and measuring the displacement amount, and taking the difference from the displacement amount before rotation,
By obtaining a value close to the original displacement amount as the third displacement amount without being affected by the distortion of the optical system and moving the detection center of the detector by the field of view corresponding to the third displacement amount, The detection center is made to coincide with the original center of the optical system. As a result, there is almost no measurement error due to distortion of the optical system, and a highly accurate shift amount can be measured.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a registration measuring apparatus according to an embodiment to which an adjusting method of a positional deviation amount measuring optical system according to the present invention is applied.

FIG. 2 is a flowchart of position adjustment processing of the center of the optical system and the center of the detector.

FIG. 3 is an explanatory diagram of a relationship between a distortion amount and a deviation amount of a registration pattern, where (a) is
FIG. 6B is an explanatory diagram of a registration pattern before rotation, and FIG. 7B is an explanatory diagram of a registration pattern after rotation by 180 °.

FIG. 4 is an explanatory diagram of measuring a shift amount by shifting a measurement point from the center of the visual field.

5 is an explanatory diagram of an example of the measurement result in FIG.

6A and 6B are explanatory views of a registration pattern, where FIG. 6A is an example in which a resist pattern is inside the etching pattern, and FIG. 6B is an example in which the resist pattern is above the etching pattern; (c) is an example in which the etching pattern is inside the resist pattern.

FIG. 7 is an explanatory view of the arrangement of chips and registration patterns on a wafer and the detection signal of a detector, (a) shows the arrangement of chips and registration patterns on a wafer, (b) shows a detection signal.

[Explanation of symbols]

1 ... Objective lens, 2a, 3a ... Relay lens, 4, 55
... Half mirror, 5 ... Illumination optical system, 6a, 6b ... Field setting variable slit, 7 ... Wafer chuck, 8 ... XYZ moving stage, 9 ... Wafer, 10, 11 ... CCD linear sensor, 15 ... A / D conversion circuit ( A / D), 16 ... Image memory, 17 ... High-speed numerical operation processor, 18 ... Focus controller, 19 ... MPU, 20 ... Control device, 21 ...
Memory, 22 ... Bus, 30 ... Registration pattern, 31 ... Etching pattern, 32 ... Resist pattern, 33 ... Inner frame of outer pattern, 50 ... Light source, 51 ...
Light quantity adjusting filter, 52 ... fiber, 53 ... diaphragm mechanism,
54 ... Field stop.

Claims (3)

[Claims] 1. A detector having a center located in the center of a field of view and receiving light from a position shift amount measurement pattern and generating a detection signal representing the position shift amount, the position shift amount being determined by the detection signal. In a method of adjusting a measurement optical system in a position shift amount measuring device for measuring, a shift mechanism for moving a detection center of the detector is provided, and a shift amount obtained by measuring a shift amount of the position shift amount measurement pattern is first. Of the positional shift amount, the shift amount obtained by rotating the position shift amount measurement pattern by 180 ° and measuring the shift amount is referred to as a second shift amount, and the first shift amount and the second shift amount. Is obtained as a third shift amount, and the position shift amount measuring optical for moving the center of the detector by the moving mechanism according to the third shift amount by the field of view corresponding to the third shift amount. How to adjust the system. 2. The method for adjusting a position shift amount measuring optical system according to claim 1, wherein the third shift amount is 1/2 of a difference between the first shift amount and the second shift amount. 3. A detector having a center located at the center of the field of view and receiving light from a displacement amount measurement pattern to generate a detection signal representing the displacement amount, the displacement amount being determined by the detection signal. In a position shift amount measuring device for measuring, a shift mechanism for moving a detection center of the detector and a shift amount of the position shift amount measurement pattern are measured as a first shift amount, and the position shift amount measurement pattern is set to 180 °. A deviation amount measuring unit that rotates and measures the deviation amount as a second deviation amount, and 1/2 of a difference between the first deviation amount and the second deviation amount is calculated as a third deviation amount. A positional deviation amount measuring device comprising: a means and a moving means that controls the moving mechanism according to the third deviation amount to move the center of the detector by a field of view corresponding to the third deviation amount.