JPS60147741A - Processor and its monitoring method - Google Patents

Abstract

PURPOSE:To correct the change of reference length accurately so that the change of the reference value is calculated as a half of a detected value and to contribute to the system stabilization by arranging an off-axis microscope symmetrically with a projection lens. CONSTITUTION:A reference A of a detecting system 15 and an alignment mark AM2 are catched, and if a difference is detected between the reference A in the directing system 15 and the mark AM2, a signal corresponding to the difference is outputted. At that time, the positional shift in the x axis direction is measured or the XY stage is moved along the x coordinate until the mark AM2 coincides with the reference A. The alignment mark AM2 is matched with a reference C of a detecting system 17, an wafer is moved by 2L' from the reference C along the y coordinate and the deviation between the reference of a detecting system 18 and the alignment mark AM2 is measured. A half of the error is stored in a control device 22 as a correcting value, and when the detecting system 17 or 18 is used form the detection of the alignment mark, the correcting value is used to determined the moving value. Thus, the change in the reference length can be accurately corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Background) The present invention relates to the removal of errors in a device for accurately moving and positioning an object whose position has been fixed in advance to a specified position in a detection system, and particularly relates to the removal of errors in a device for positioning an object whose position is fixed in advance in a detection system. Among mask aligners that transfer images onto wafers, this is suitable for eliminating alignment errors in step-and-repeat transfer devices that perform off-axis wafer alignment. - (Prior Art) In recent years, a step-and-repeat type exposure device, a so-called stepper, has come into frequent use as a type of fine addition f in 10 manufacturing. With a stepper, it is very difficult to align the pattern on the wafer that has been processed up to the previous process and the pattern that is about to be exposed.
i! It becomes a factor. The off-axis method and the TTL method are known as alignment methods. Although TTI is limited by the projection lens used to transfer the reticle pattern onto the wafer, it has the advantage of being able to match patterns directly. In contrast, in the or-axis method, another reference point is provided at a predetermined distance from the projection lens, and the wafer is first aligned with respect to that position. After that, the wafer is fed a predetermined distance using a high-precision position detection means such as a laser interferometer, and exposed using a projection lens.In the 5° off-axis method, detection is performed at a position different from the projection lens, so the projection lens It has the advantage of not being subject to any restrictions.

However, in this method, since there are multiple reference points, long-term fluctuations in the distance between them (reference length) poses a problem. That is, the distance between the reference point of the projection lens and the reference point of the detection position of the wafer is on the order of 0.1 μm, but is never constant due to thermal factors, etc., and varies over time. This change in the reference length immediately leads to a deterioration in alignment accuracy in the projection lens that reduces and projects the image of the reticle (not shown) (original plate on which the integrated circuit pattern is drawn) onto the silicon wafer 6. is its optical axis. 2 is the microscope objective lens of the detection system, and x2 is its tip axis. It is also assumed that an alignment mark (not shown), such as a crosshair, is drawn on the wafer 6. Here, , the distance between the optical axis x1 of the projection lens and the optical axis x2 of the microscope objective lens, that is, the reference length, is strictly determined.The detection system is, for example, a photoelectron microscope (U.S. Pat.
0097) T, internal 0:) 1, and then step feed by an amount commensurate with the chip size for each exposure shot. Therefore, variations in the reference length directly lead to deterioration of alignment accuracy, which significantly affects product yield.

It should be noted that the automatic detection system is not limited to a photoelectron microscope, and other types may be used, and the alignment of the crosshairs can also be performed manually by observing with an eyepiece or a TV monitor. The form of the mark is not limited to this either. In addition, this method of determining the density of seeding is not limited to optical projection type steppers, but is also applied to the positioning of equipment that forms butter on Ueno using loads and heavy particles, and even to the positioning of machining equipment such as precision hole drilling. .

(Purpose) The purpose of the present invention is to monitor and recognize fluctuations in a reference length using a device that includes a step of detecting the position of an object using a detection system that is separated by a reference length from a main system such as a projection system, or to detect the effects thereof. The goal is to eliminate the

(Embodiment) Hereinafter, an embodiment of the present invention will be described using FIG. 2 showing the planar arrangement and FIG. 1g6 showing the configuration viewed from an angle. However, when implementing the present invention, if an alignment mark with an X component and a Y component is used, it is basically sufficient to provide one set of detection systems, but in this example, quality compensation is more important. Figure 10 shows a reduced projection lens, and 11 shows a reticle 112 having cross-shaped alignment marks AM1 and AM2 spaced apart by a prescribed length, but they may also be provided on an XY stage. The XY stage 14a can move in two directions: the X coordinate direction, the z direction, the parallel ff, and the Y coordinate directions, that is, step movement and rotational (θ) movement.

15.1<5 and 17.18 are detection systems such as photoelectron microscopes, and output is performed according to the difference between the inside of the detection system, the X and Y references, and the crosshair. The detection systems 15 and 16 are arranged so that the centers of the reference person B are symmetrical with respect to the optical axis 0 of the projection lens 10, and the distance between the optical axis O and the center of each detection system is determined to be the reference length. N・ru.

It is desirable that the imaginary line connecting centers A and B be parallel to the X coordinate.

In addition, the detection systems 17 and 18 are symmetrical with respect to the optical axis 0 of the projection lens 10, and the distance between the centers of the optical axis 0 and the center of each detection system is set to L, and an imaginary line connecting the centers C and D is set. is arranged so that it is perpendicular to the imaginary line connecting centers A and B. However, 1 detection systems 17 and 18 are used unless the detection systems 15 and 18 are tested while being biased in the y-coordinate direction, or when it is necessary to independently determine the position of the alignment mark in the x-coordinate and y-coordinate direction. Can be omitted.

Reference numerals 20 and 21 each indicate a precision length measuring device, which measures the distance along the y-coordinate on the Z-coordinate of the XY stage, that is, the wafer. 22 is a control device which, according to the command signal from the operating device 24,
Command to move twice the reference length, measure the difference between the alignment mark and the detection system reference, generate a signal to make the difference zero, and correct the reference length using the variation in the reference length as a compensation value. It has functions such as generating signals corresponding to , and even generating signals for step movement. The movement of the XY stage 14 is accurately controlled by feeding back the measurement values of the length measuring devices 20 and 21 to the control device 22. Reference numeral 26 denotes a drive mechanism for the XY stage 14, which has a function of moving the XY stage in the X coordinate direction, the y coordinate direction, and the rotational direction.

Now, if the reference length of this device changes due to some factor, for example, a thermal factor of the entire device, the effect will be isotropic on all the relative relationships between the projection lens 1 and the detection systems 15 to 18. It can be assumed that it is effective. Therefore, the effect appears as half of the value obtained by measuring the distance between the sensing systems and subtracting twice the reference length from this (a negative signal occurs when the sensing systems are close together). For example, a change in the reference length in the S coordinate direction results in a change in the distance between the projection lens 10 and the detection system 15.

The action will be explained below. First, align the alignment mark AM1 with the reference person of the zero detection system 15 that removes the rotation error of the wafer 13, and then move the XY stage 14 accurately by a specified mark interval <1 along the y coordinate. The detection system 15 then captures another alignment mark AM2, and if there is a difference between the reference within the detection system 15 and the alignment mark AM2, it outputs a signal corresponding to the difference. At this time, the detection system itself may measure the positional deviation in the two coordinate directions, or the reference person and the 7-line fist! - The XY stage may be moved along the S coordinate until the person M2 matches, and the positional deviation ΔX may be measured by the amount of movement.

Here, a rotational error is detected as 6-'ran (Δ-1./l), and if the XY stage 14 is rotated by this angle θ, the rotational error of the wafer is eliminated. However, the above process is unnecessary if the positioning of the workpiece is one-dimensional.

Next, when the alignment mark AM2 matches the reference of the detection system 15, the drive mechanism 26 is operated to move the XY stage 14 along the X coordinate so that the alignment mark AM2 matches the reference mark AM2. The deviation amount 2ΔL is subtracted from the amount of movement when the XY stage 14 is moved until the position is reached.

! Since the semi-length variation is isotropic, the reference length II'iL from the optical axis of the projection lens 15 to the optical axes of the detection systems 15 and 16
There is +ΔL″′C.

The control device 22 temporarily stores this result L+ΔL, and moves the XY stage 14 from the detection system along the The amount of movement required is calculated, the drive mechanism 23 is operated according to the calculated amount, the XY stage 14 is set at the initial exposure position, and after exposure, a well-known step-and-repeat movement is performed.

In addition, for the second and subsequent wafers, use either detection system 15 or 16 to rotate the wafer, then align the 72 moment mark with that detection system, and set the reference length L + ΔL.
The wafer is moved to the initial exposure position according to information that takes into account the

On the other hand, the verification of reference length variations between the detection systems 17 and 18 and the projection lens 1 can also be performed using the same procedure as described above. That is, align the 7-point mark AM2 with the reference C of the detection system 17, move the wafer 2 L' along the y-coordinate, and measure the deviation between the reference of the detection system 18 and the 72-point mark. do. Half of the error at this time is stored in the control device 22 as a correction value, and when the detection system 17 or 18 is used to detect the alignment mark, this value is used to determine the amount of movement. In addition, the wafer is moved orthogonally by this correction value and the correction value in the X coordinate direction, and the alignment is performed using the detection thread 15.
When searching for the i-axis, if there is an error in the y-coordinate direction, it can be seen that the detection system 15 is deviated from the virtual line passing through the optical axis of the projection lens, and this can be used to compensate for it. The aforementioned test is performed once a day or once an hour.

(Effects) As stated above, the reference length, which is the most important in off-axis 1σ alignment, is constantly checked by the method of the present invention, and long-term fluctuations can be easily addressed. It will be corrected. Furthermore, by arranging the off-axis microscope symmetrically with respect to the projection lens, it is possible to correct changes in the & semi-length with high accuracy. Change in standard length lol
Even in the case where J is asymmetric, the amount of change in the reference length is calculated by averaging the values detected by the two bare microscopes. can be said to be large. In the above example, the optical axis of the detection system is arranged on a line passing through the optical axis of the projection lens, but if two detection systems are installed across the optical axis of one projection lens, If the detection system is arranged symmetrically with respect to a straight line passing through the optical axis, the effects of the present invention can be obtained.

[Brief explanation of the drawing]

(A) (B) Figure 1 is a diagram for explaining a conventional example. Figure 2 is a plan view of an embodiment of the present invention, and Figure 3 is a perspective view. In the figure, 10 is a projection lens (main system), 11t;t reticle,
16 is a wafer, 14 is an XY stage, 15 to 18 are detection systems, and 22 is a control device. Applicant Canon Co., Ltd. (A) To? figure

Claims (6)

[Claims] (1) Main system and multiple detection systems for detecting the position of an object arranged symmetrically with respect to the main system, a moving means for moving the object in a wide fixed amount, and a main system related to the output of the detection system. A processing device equipped with means for calculating the interval error of the detection system. (2) The processing device 0 according to claim 1, in which four detection systems are arranged. (3) The processing device according to claim 1, wherein the virtual lines connecting two of the detection systems are perpendicular to each other. (4) The processing device according to claim 1, wherein the main system is a projection system that projects an integrated circuit pattern. (5) Main system and measurement system, including a step of symmetrically arranging multiple detection systems for detecting the position of an object with respect to the main system, and a step of measuring the interval between the symmetrically arranged detection systems. □ Monitoring method for monitoring interval deviation between (6) The monitoring method 0 according to claim 1, which is a projection system that projects the main integrated circuit pattern.