JPH08285522A - Measuring method of position and measuring apparatus of position using the same - Google Patents

Abstract

PURPOSE: To reduce a linearity error with hardware modification minimized, by a method wherein a wafer mark being an object of measurement is measured at a plurality of positions being different in the relative relationship in one pixel of a CCD image sensing element and measured values are averaged. CONSTITUTION: A wafer 5 fixed by suction on a wafer chuck 8 is sent in by a wafer stage 6 so that a wafer mark may come in a visual field of observation of an off-axis microscope 7. A plurality of wafer marks are formed beforehand on the wafer and these are measured by the microscope 7 by driving the stage 6. In the microscope 7, the wafer mark is measured at a plurality of positions being different in the relative relationship in one pixel of a CCD image sensing element and measured values obtained thereby are averaged. The position to an apparatus of the wafer 5 on the wafer chuck 8 is determined on the basis of the coordinates of the stage 6 and a positional slippage of the wafer mark from a microscope reference at each time point of measurement, and a projected image of a reticle 3 and a pattern on the wafer are aligned in position with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position measuring method and a position measuring apparatus using the same, and more particularly to an exposure apparatus for exposing a photosensitive layer coated on a substrate of a semiconductor wafer, and more particularly to a pattern formed on the wafer. The present invention is suitable for an exposure apparatus having a function of detecting a position with high accuracy and aligning an image of a pattern of a reticle with respect to the pattern with high accuracy, and for performing general position measurement.

[0002]

2. Description of the Related Art Conventionally, in an exposure apparatus for manufacturing a semiconductor device such as a stepper, when aligning a pattern formed on a reticle and a pattern formed on a wafer, they are first mounted on a wafer stage. The alignment mark (wafer mark) formed on the wafer is guided under the microscope in the exposure apparatus to perform measurement. In the measurement, the amount of displacement of the wafer mark with respect to the reference of the microscope is detected. At the same time, the position of the wafer is determined by referring to the wafer stage position at that time, and then the method of aligning with the image of the reticle is generally used. Done.

When measuring the amount of displacement of the wafer mark with a microscope, the image of the wafer mark is usually measured by an objective lens,
A relay lens and an erector lens are used to magnify and project on the image sensor. Although an image pickup tube or a solid-state image pickup element is used as the image pickup element, CCD is currently used because of its advantage in measurement accuracy such as coordinate accuracy, stability, and simultaneity of in-screen measurement, and high reliability. In many cases, a solid-state image sensor called as.

The wafer image enlarged and projected on the CCD is CC
Each pixel of D is converted into an electric signal proportional to the received light, and the signal is processed to measure the amount of positional deviation of the wafer mark. The physical resolution of the measurement system is determined by the pixel pitch of the CCD and the imaging magnification of the microscope. Since the standard number of pixels of CCD is about 500 × 500 and the screen size required for measurement is about 100 to 200 μm square, the physical resolution is only about 0.2 to 0.4 μm. Therefore, in practice, a method is adopted in which a plurality of discrete data obtained for each CCD pixel pitch of the wafer mark are selected and interpolated to improve the resolution.

Various image processing methods that have been proposed in the past, such as A. The signal waveform is analogized from the selected data and the peak position is calculated. B. The area is calculated from the waveform shape of the signal, and the position of the center of gravity is calculated. C. Calculate the center position where the left and right slopes of the waveform have the highest symmetry. Etc., and apply these to 1/5 to 1/1 / the physical resolution.
A measurement resolution of about 10 can be achieved.

[0006]

[Problems to be Solved by the Invention] However, the resolution of the measurement system is required to be higher and higher. Since the conventional interpolation method calculates from a plurality of points selected with a relatively coarse sampling pitch, the number of measurement points becomes relatively insufficient when the actual wafer signal is detected by the measurement system. Due to the positional relationship with the pixel, the measured value fluctuates on the order of concern in terms of accuracy.

This is a phenomenon called linearity error due to insufficient measurement resolution, which will be described in detail later. The pixel pitch of the CCD is sufficiently small with respect to the optical signal waveform of the wafer mark, which is the object to be measured, and is sufficient for the required resolution. It can be ignored if different measurement points can be taken. In this case, the same measured value can be obtained regardless of the position of the pixel position of the CCD with respect to the optical signal waveform. However, for that purpose, it is necessary to increase the image formation magnification of the microscope or to use a CCD with high resolution, which is not practical from the viewpoint of the amount of light and cost.

[0008]

According to the present invention, in order to reduce a linearity error caused by a coarse measurement pitch, a plurality of wafer marks to be measured have different relative relationships within one pixel of an image pickup device such as a CCD. It is characterized in that the measurement is performed at the position, and the final measurement value is obtained by performing calculation processing such as averaging the plurality of measurement values.

Actually, the number of measurement points for calculation processing is M,
When the pixel resolution of the CCD on the surface to be measured is P,
The measurement is performed by P / M equivalently in one pixel of the CCD, at M points that are deviated, and processing such as averaging each measurement value is performed. Equivalent here means that the modulus is considered at the CCD pitch P which is the pixel resolution, and for example, the driving amount when driving the stage is also converted by taking the modulus. Particularly, if M is a multiple of 2, it is possible to reduce the linearity error with a small number of times and with high accuracy.

Further, when the measurement is performed by using a plurality of wafer marks, the pitch of the wafer marks is W _p ,
Assuming that the number of marks is m, the wafer mark with W _p ≈P × N ± P / m (where N is an integer) is measured. Since it shifts by P / m as it goes, it is possible to obtain the above-described effect of the shift, and it is possible to accurately reduce the linearity error. Also at this time, it is efficient to set m to be a multiple of 2.

[0011]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention. In this embodiment, the case where the present invention is applied to an exposure apparatus for manufacturing a semiconductor device having a positioning function is shown.

In the figure, 1 is a mercury lamp as an exposure light source, 2 is an illumination system for illuminating a reticle, 3 is a reticle, 4 is a projection lens, and 5 wafers are adsorbed and fixed to a 8 wafer chuck. On the wafer, the alignment mark shown in FIG. 6 patterned in the previous step (hereinafter referred to as wafer mark)
Are formed in advance.

Referring again to FIG. 1, reference numeral 6 denotes a wafer stage, the position of which is detected and controlled by a laser interferometer and an arithmetic and control unit (not shown). An off-axis microscope 7 measures the position of the wafer mark on the wafer 5 by comparing it with a microscope reference, and measures the amount of positional deviation.

The wafer 5 coated with the photosensitive agent is carried onto the wafer chuck 8 by a wafer carrying system (not shown). The wafer 5 sucked and fixed to the wafer chuck 8 is sent by the wafer stage 6 so that the wafer mark is within the observation field of the off-axis microscope 7. A plurality of wafer marks are formed in advance on the wafer, and the wafer stage 6 is driven to measure the plurality of marks with the microscope 7. The position of the wafer 5 on the wafer chuck 8 with respect to the apparatus is determined from the coordinates of the wafer stage 6 at each measurement point and the amount of displacement of the wafer mark from the microscope reference. Thereafter, the wafer stage 6 is driven by a predetermined amount, and the reticle 3
And the pattern on the wafer are aligned.

The off-axis microscope 7 includes an objective lens 71,
Relay lens 72, erector lens 73, CCD7
4, the epi-illumination system 75. The wafer mark illuminated by the illumination system 75 forms an image on the CCD 74 through the objective lens 71, the relay lens 72, and the erector lens 73.

FIG. 5 schematically shows the relationship between the formed optical image of the wafer mark and the CCD.

FIG. 2 is an enlarged view showing the relationship between the optical signal waveform of the wafer mark and the measurement points of the CCD for discrete measurement for each pixel. When the pixels of the CCD are symmetrically arranged with respect to the peak of the optical signal waveform shown by the solid line as shown in FIG. 2A, the signal waveform estimated from the CCD measurement value and the optical waveform are It is an approximate form and no calculation error occurs. However, when the pixels of the CCD are not symmetrically arranged with respect to the peak of the optical signal as shown in FIG. 2B, the signal waveform indicated by the broken line estimated from the measurement of the CCD is different from the optical waveform of the solid line. Result in different shapes, and measurement errors occur. Since the relative positional relationship between the CCD and the optical signal waveform cannot be properly determined in advance, the actual measurement is performed in the state of FIG. 2A or the state of FIG. 2B. It is not possible for the device side to make a judgment as to whether or not there is something.

FIG. 3 shows the influence of the above-described CCD sampling, and is a relationship diagram between the mark movement amount and the wafer mark measurement value when the wafer mark is moved. If there is no error, the measured value will be on a straight line, but a measured error will occur due to the relationship between the pixel position and the symmetry of the optical signal waveform, and the measured value will fluctuate in the pixel pitch cycle. This is a linearity error.

FIG. 4 (A) is a diagram in which the linear component is removed from FIG.
The linearity error generated when the wafer position is moved by the pixel is displayed.

In this embodiment, in order to reduce such linearity error, the wafer is driven a plurality of times in a direction orthogonal to the optical axis of the off-axis microscope system, which is a measurement optical system, and then measured. The feature is that the position of the wafer mark is accurately measured from the measured value and the position of the wafer monitored by the interferometer.

For example, in the case of performing the measurement twice in this embodiment,
The first time, the wafer mark is measured at an arbitrary position on the stage, and the second time, the wafer is measured by step-driving the wafer by an amount corresponding to 1/2 of the pixel pitch P on the wafer. The position of the mark can be obtained by calculating the average value of the first and second times after converting the drive amount of the wafer.

Here, the positions of the first measurement are A1, B1,
If C1 and D1 are set, the measured values at positions driven by P / 2 corresponding to these are A2, B2, C2 and D2, respectively.
Becomes Due to the periodicity, the order of subscripts 1 and 2 can be exchanged without any problem.

FIG. 4 (B) shows the relationship between the stage coordinate position and the linearity error of the average value of the wafer mark measurement when such an averaging is performed twice. FIG.
Corresponding to the shape of the linearity error curve of (A), FIG.
In (B), it can be seen that the cycle of the error curve becomes 1/2 and the absolute value of the error also decreases.

In FIG. 4C, the step amount of the wafer is set to 1/4 of the pixel pitch, and measurement is performed four times while driving the wafer mark at each position. The measured values of the four wafer marks are shown. It shows the relationship between the stage coordinate position obtained by averaging after subtracting the drive amount and the linearity error of wafer mark measurement. In this case, the measurement positions added in the previous two measurements are A3 and A, respectively.
4, B3, B4, C3, C4, D3, D4, and FIG.
It is shown in (A). Taking the average value of 4 points, the cycle of the error curve is now 1/4 of the initial cycle of Fig. 4 (A), and it can be seen that the absolute value of the error is smaller than that of the case of averaging twice. .

Generally, when averaging randomly measured values of two or four points, the peak value of the linearity error is statistically calculated for one point of data.

[0026]

[Equation 1] It is known to be reduced to.

When there is a strong periodic correlation between measured values as in the present invention, the averaging effect is more remarkable, and when the average value of 2 points is used, the average value of about 1/3 and 4 points is obtained. It was found that the measurement error can be efficiently reduced to about 1/10 when using.

In this embodiment, the pixel pitch on the wafer surface of the CCD is P, the number of averaged measurement values is M, and the drive amount of the stage is P / M. However, the drive amount of the stage is as described above. Since the correction is applied, the same result can be obtained even if the stage drive amount is measured as an amount obtained by algebraically adding P / M to an integer multiple of the pixel pitch, that is, P × N ± P / M (N is an integer). . This is because the same error occurs due to the periodicity even if the pixel pitch is moved by an integral multiple.

To further generalize the description, when the modulus is taken in pixel units, as shown in FIG.
The most important point of the present embodiment is to perform measurement by driving so as to be distributed at equal pitches within the pitch of one pixel. In terms of processing, it is efficient that M is a multiple of 2.

Further, in the above-mentioned Example 1, the combination of the wafer mark and the off-axis microscope was taken as an example. Similarly, the reticle mark, the reference mark, etc. are observed with the TTL microscope, the reticle microscope, etc., that is, the position where the mark is captured as an image. The method of the present invention can be directly applied to a microscope system for measuring.

In the first embodiment, the method of driving the mark for measurement has been described. Conversely, the measurement can be performed by moving the microscope while the mark is fixed while the relationship between the mark image and the pixel is relatively moved. The same effect can be expected.

The second embodiment of the present invention applies the drive measurement method of the present invention to the baseline measurement of a semiconductor exposure apparatus. The baseline is the distance from the optical axis of the projection lens of the semiconductor exposure apparatus to the reference position of the microscope that measures the wafer mark.

Usually, in the alignment of the wafer with respect to the projected image of the reticle, the wafer mark is first measured with a microscope as a deviation amount with respect to the microscope reference, and a baseline amount measured beforehand is added to this value to add a projection lens of the projection lens. It will be sent down. If there is a measurement error in the baseline, a shift corresponding to the measurement error will be added over the entire surface of the wafer. Therefore, it is necessary to make the baseline measurement more accurate than the wafer measurement, and it is necessary to perform the accurate measurement even if it takes some time.

Referring again to FIG. 1, in the baseline measurement method, first, the wafer mark on the wafer 5 is sent under the projection lens 4. The TTL microscope 9 measures the amount of positional deviation D _ttl1 between the alignment mark (reticle mark) previously provided on the reticle 3 and the wafer mark, and at the same time measures the position P _ttl1 of the wafer stage 6.

Subsequently, the wafer stage 6 is moved to feed the wafer mark under the off-axis microscope 7, and the amount of positional deviation D _oa1 of the wafer mark with respect to the reference of the off-axis microscope and the stage position P _oa1 are simultaneously measured. At this time, the baseline measurement value L _base1 is _obtained by L _base1 = (P _ttl1 −D _ttl1 ) − (P _oa1 −D _oa1 ). This is the first measurement, and the subscript 1 indicates the first measurement.

Next, the wafer 5 is _fed again below the projection lens 4, and the TTL microscope 9 simultaneously measures the positional deviation amount D _ttl2 between the reticle mark and the wafer mark and the stage position P _{ttl2 at} that time. However, the stage position _{Pttl2 of} this time is shifted by S1 with respect to the previously measured measurement position _Pttl1 .

The shift amount S1 is given by S1 = P1 / M1 where P1 is the pixel resolution in terms of the wafer surface of the TTL microscope and M1 is the number of times the baseline measurement is repeated.

When the measurement with the TTL microscope is completed, the wafer 5 is subsequently _fed again under the off-axis microscope 7, and the positional deviation amount D _oa2 of the wafer mark with respect to the reference of the off-axis microscope and the stage position P _oa2 are simultaneously _measured. To be measured. The stage position P _{oa2 at} this time is shifted by S2 with respect to the previously measured measurement position P _oa1 .

The shift amount S2 is S2 = P2 / M1 where P2 is the pixel resolution in terms of the wafer surface of the off-axis microscope.

The baseline measurement value L _base2 this time _{L base2 = (P ttl2 -D ttl2} ) - obtained in (P _oa2 -D _oa2).

The baseline measurement operation for measuring the position shift of the mark and the stage position is performed by shifting the position of the mark by S1 for the TTL microscope and S2 for the off-axis microscope from the previously measured stage position each time.
The final baseline amount is obtained by repeating the above times and averaging the values of the M1 baselines.

With such a method, the influence of the linearity error can be reduced, and the accurate baseline amount can be measured. If the wafer and the reticle are aligned and exposed using the baseline amount, the reticle pattern can be transferred onto the wafer more accurately.

In the present embodiment, the measurement with the TTL microscope and the measurement with the off-axis microscope are alternately performed. However, the measurement with the TTL microscope is performed M3 times while changing the stage position by S3, and the off-axis microscope. The same effect can be obtained if the measurement using is also repeated M4 times while changing the stage position by S4 each time, the measured values of each microscope are averaged separately, and the baseline is calculated by the difference.

In this case, S3 and S4 are given by S3 = P1 / M3 S4 = P2 / M4 as is apparent from the above description.

The third embodiment of the present invention is an alignment deviation measuring device for obtaining a position deviation amount using a resist pattern formed on a wafer.

FIG. 7 is a schematic diagram thereof. A microscope for measuring a wafer, a wafer mounting chuck, and a stage for moving the wafer mounted on the chuck to a desired position are formed on the main body. The wafer measuring microscope has the same configuration as the off-axis microscope 7 shown in FIG.

A reticle image aligned with the wafer pattern is projected and transferred by the exposure device onto the wafer on which the pattern is formed and the resist is applied on the pattern.
When the wafer is developed, a resist pattern corresponding to the reference pattern is formed on the reference pattern for measuring the positional deviation, which is provided on the wafer in advance.

FIG. 8 shows this state. Inside the quadratic measurement reference pattern on the wafer, a quadrilateral resist pattern having a size slightly smaller than the reference pattern is formed. The alignment accuracy of the transfer pattern of the resist with respect to the wafer pattern is monitored by measuring the distance between the parallel sides of these two patterns.

The wafer on which the resist image of the transfer pattern is formed is carried onto the stage of the alignment deviation measuring device, and the measurement pattern portion on the wafer is sent under the microscope by the stage. The reference pattern and resist pattern on the wafer are the objective lens of the microscope, the relay lens,
The position of each edge is measured by image processing by enlarging and projecting on a CCD camera through an erector lens.

The distance from the first edge position of the measurement reference pattern on the wafer to the first edge position of the resist pattern is L1, and the second edge position of the resist pattern to the second edge position of the measurement reference pattern on the wafer. Is L2, (L1−L2) / 2 is the misalignment of the transferred resist pattern with respect to the wafer pattern.

As the demand for measurement accuracy becomes stricter, the required pixel resolution is relatively higher than the required resolution, and the precision is becoming insufficient. The situation during this time is the same as in the semiconductor exposure apparatus described so far even in the alignment deviation measuring apparatus.

Therefore, also in this embodiment, when the pixel resolution is not sufficient for the required accuracy, the stage is intentionally driven by a predetermined amount to shift the pattern position with respect to the pixel position, and the average value is obtained by measuring at a plurality of positions. The linearity error can be reduced.

The stage drive amount D _p at that time is given by D _p = P × N ± P / M (N is an integer), where M is the average number of times and P is the pixel resolution in terms of the wafer surface.

As described above, it becomes possible to measure the alignment deviation amount with high accuracy by combining the minute driving of the stage with the microscope measurement. Also in this case, in order to move the relative relationship between the optical image and the CCD pixel, in addition to the stage, an optical system such as a microscope or means for moving the CCD can be used.

In the above-described embodiments, one mark or one edge has been used as the mark to be measured.
However, the measuring method and apparatus of the present invention have a plurality of marks instead of a single mark, and the positions of the marks are the same as those obtained by measuring a plurality of positions with respect to a pixel, for example, in FIG. Thus, by calculating the average value of the measured values of the plurality of marks, the linearity error can be improved as before.

For example, when the wafer marks are a plurality of equidistant marks having a pitch W _p , the number of marks is m,
If W _p ≈P × N ± P / m (N is an integer) where P is the pixel pitch in terms of the wafer surface, equivalently, the same effect as the multiple measurements in FIG. 4 can be obtained by one measurement. You can Further, practically, the value of m is a multiple of 2, which is advantageous in processing.

On the contrary, when it is necessary to fix the pitch of the wafer mark, it is possible to obtain the same effect by changing the image forming magnification so as to satisfy the above relational expression of W _p .

As described above, according to the present invention, when the size S of the pixel on the object to be measured and the number of times of measurement are M in a state where the modulus is taken in pixel units, the measurement can be performed simultaneously or with time-dependent S / M. The feature is that the linearity error is reduced by a simple calculation process such as performing the measurement at a pitch and averaging the measured values.

Therefore, in order to obtain the above effect, various means for changing the relative position of the pixel and the measurement sample, for example, driving the stage, driving the microscope optical system, changing the microscope magnification, driving the CCD itself, devising the mark. Etc. are included.

[0060]

As described above, according to the present invention, an object to be measured is equivalently measured at a plurality of positions at equal intervals in one pixel, and calculation processing such as averaging is performed on the measured value. By adding it, it was possible to significantly reduce the linearity error without making any hardware changes or minimizing the hardware changes. In response to the ever-increasing demand for improved measurement accuracy, the problem of insufficient resolution of the measurement points that the current measurement system has is to increase the magnification of the microscope system by a method of averaging, which is shifted, rather than simply performing multiple measurements. Since it can be solved without using an expensive high-resolution CCD, it can be easily applied to the current system and the improvement effect is great.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an exposure apparatus for a semiconductor manufacturing element to which the present invention is applied.

FIG. 2 is a diagram showing a relationship between a signal waveform of a mark and a measurement point.

FIG. 3 is an explanatory diagram of linearity error.

FIG. 4 is a diagram showing a linearity error and a measurement point within one pixel.

FIG. 5 is a diagram showing a relationship between a measurement object and a CCD.

FIG. 6 is an example of a wafer pattern to be measured.

FIG. 7 is a configuration diagram of an alignment deviation measuring device to which the present invention is applied.

FIG. 8: Measurement pattern for alignment deviation measuring device

[Explanation of symbols]

 1 exposure light source (mercury lamp) 2 illumination system 3 reticle 4 projection lens 5 wafer 6 wafer stage 7 off-axis microscope 8 wafer chuck 9 TTL microscope 71 objective lens 72 relay lens 73 erector lens 74 CCD 75 epi-illumination system

Claims (12)

[Claims] 1. When measuring the position of an object by using an image sensor that detects an image at a fixed sampling pitch, the position of the object is measured at a plurality of positions relatively moved with respect to the image sensor, and the measurement is performed. A position measuring device, wherein the position of the object is determined by calculating a value and a relative movement at that time. 2. When the size of one pixel on the object plane is P for the plurality of measurement positions and M for the number of the plurality of measurement positions, the relative movement amount of the first item is divided by the sampling pitch. 2. The position measuring device according to claim 1, wherein the remainder when hit is about P / M. 3. The position measuring device according to claim 2, wherein the plurality of measurements are performed a plurality of times. 4. The position measuring device according to claim 2, wherein the plurality of measurements are performed simultaneously. 5. The object is mounted on a stage movable in a direction orthogonal to an optical axis of a measuring optical system for measuring the object, and the object is measured by moving the stage. 2 position measuring device. 6. The position measuring device according to claim 2, wherein a measuring optical system for measuring the object is moved when the object is measured. 7. The position measuring device according to claim 2, wherein the value of M is a multiple of 2. 8. The measurement target mark of the object has a pitch W _p
When the size of one pixel of the image sensor on the object plane is P, W _p ≈P × N ± P / m (N is an integer) The position measuring device according to claim 2, which is characterized in that. 9. The position measuring device according to claim 8, wherein the value of m is a multiple of 2. 10. The position measuring device according to claim 9, wherein a magnification of a measuring optical system for measuring the object is adjusted when the object is measured. 11. When measuring the position of an object using an image sensor that detects an image at a constant sampling pitch, the position of the object is measured at a plurality of locations that have moved relative to the image sensor, A position measuring method characterized in that the position of the object is determined by calculating a measured value and a relative movement at that time. 12. The plurality of measurement positions are 1 in the object plane.
The remainder when the relative movement amount of the first term is divided by the sampling pitch is approximately P / M, where P is the size of the pixel and M is the number of the plurality of measurement positions. Item 11 position measurement method.