JPS62181430A - Calibrating method of exposure apparatus - Google Patents

Abstract

PURPOSE:To perform only one wafer positioning in exposing one wafer and to make it possible to perform relative positioning of a mask and the wafer highly accurately, by moving a target mark and a detecting mark on the mask in a visual field so that both marks are aligned, and obtaining the coordinate position. CONSTITUTION:Photoelectric microscopes 25 and 26 correspond to inherent points 10. When the positions of the microscopes are not changed with respect to a static coordinate system with a reducing lens 3 and a laser interference- length measuring system as references, accurate mask alignment is always performed. In reality, however, change occurs and therefore calibration is required. At the periphery of a mask 1, a target mark 49 and a detecting mark 50 to be aligned are provided. A moving stage 18 is finely moved so that the target mark 49 in the visual field and the detecting mark 50 on the mask 1 are aligned. The coordinate position of the moving stage 18 when the marks are aligned is obtained. Thus the relative positioning of a wafer 4 and the mask is completed by one time for one wafer, and the alignment accuracy is readily acknowledged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally aligns the positional relationship between a first figure that has already been formed and a second figure to be newly formed thereon, and creates an optical image of the second figure. The present invention relates to a method for calibrating a projection type exposure apparatus that exposes a first figure in a predetermined positional relationship, and more specifically, a projection type exposure apparatus that prints a circuit pattern on a wafer in an integrated circuit manufacturing process.

Conventionally, pattern exposure methods used for semiconductor integrated circuits and the like are roughly divided into two methods: contact exposure method and projection exposure method. The former is a method that has been used for a long time, and the configuration of the exposure equipment is simple.

Although it has the advantage of being able to expose the entire wafer at once and is more productive, it is difficult to completely adhere the mask to the entire wafer, and if a gap is created, fine circuit patterns cannot be transferred due to light diffraction. Another disadvantage is that the wafer surface is easily damaged during close contact. On the other hand, the latter method has the advantage of not damaging the wafer or even the mask since it can be exposed without contacting the wafer. However, in order to print a fine pattern using the projection exposure method, it is usually necessary to increase the reduction ratio due to the difficulty in manufacturing the projection lens, which inevitably results in a small exposure area. For example, a high-resolution lens capable of resolving a pattern with a width of 1 μm has a maximum exposure range of about 14 mmφ at a magnification of 1/10. Therefore, in order to print a larger wafer, the wafer must be sequentially stepped and exposed several times. With conventional projection exposure equipment, each step of feeding the wafer
The positioning mark on the wafer and the positioning mark on the mask are optically observed wA through a projection lens, and the mask is normally moved slightly to align the two marks for exposure. Therefore, in order to expose a single wafer, it was necessary to advance or align the position several dozen times, making the apparatus unproductive. In addition, when aligning the two marks, it is necessary to use light with a wavelength different from the wavelength of the light used during exposure so as not to expose the photoresist coated on the wafer. The device itself, including the switching mechanism, was also complex. IBM Technical Disc is an apparatus that improves the drawbacks of the conventional projection exposure apparatus, that is, a projection exposure apparatus that completes alignment with only one operation for each wafer.
Losure Bulletin Volume 13 No. 7 P181
There is a method proposed in 6.

That is, a microscope observation device dedicated to wafer positioning is provided outside the projection exposure optical system, and after the wafer is positioned with respect to the optical axis of this microscope device, the wafer is moved a certain distance and introduced into the exposure optical system. The mask and wafer are aligned indirectly. Thereafter, the wafer is precisely stepped in XY directions by a predetermined absolute amount, and exposure is performed to complete the exposure of the entire surface of one wafer.

According to this method, the wafer only needs to be positioned once before exposure, which is very productive. However, on the other hand, it is necessary to keep the absolute spatial relationship between the microscope device and the exposure optical system constant for a long period of time. Therefore, poor relative alignment accuracy between the mask and the wafer is likely to occur.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional projection exposure apparatus, and it only requires one wafer positioning when exposing one wafer, and further provides a highly accurate mask and wafer that is stable for a long period of time. The present invention provides a method for calibrating a projection exposure apparatus, which calibrates a projection exposure apparatus so as to perform relative positioning.

The prior art on which the present invention is based and the principle of operation of the present invention will be explained with reference to FIG. Although FIG. 1 shows only one axis, the same applies to the XYZ axes. The purpose here is to form an optical image of the circuit pattern 2 on the mask 1 by the microlens 3 so as to accurately overlap the pattern 5 on the wafer 4. In the conventional apparatus, a microscope optical system consisting of an objective lens 6, a reflector 7, an eyepiece 8, and an epi-illumination system (not shown in the figure), which are firmly fixed to a microlens 3, is used to illuminate the wafer 4. The wafer 4 is aligned so that the pattern 5 coincides with the intersection A of the central optical axis Q1 of the microscope optical system and the imaging plane P of the microlens 3. On the other hand, if the circuit pattern 2 on the mask 1 is on the center light @Q2 of the reduction lens 3, the pattern 5 on the wafer 4 is aligned with the intersection point 0 of the center optical axis Q2 and the plane P. In other words, by moving the wafer 4 by a certain distance AO=L1, the optical image of the circuit pattern 2 taken by the reduction lens 3 can be made to match the pattern 5 on the wafer 4. In this case, the circuit pattern 2 on the mask 1 is
2, a mask positioning mark 9 is provided on the mask 1 in advance, and the mark 9 is placed with respect to the unique position 10 on the stationary coordinate system determined from the microscope optical system and the reduction lens 3. This can be done by matching the . However, in an actual device, the distance between the microlens 3 and the mask 1 is large, about 300 to 600 mm, and even if the member that connects them is manufactured with high rigidity, temperature changes and external vibrations may cause the static coordinate system to The unique position 10 is 5 to 10 μm for several days
The extent also changes, and it is difficult to perform mask alignment with an accuracy of 0.1 to 0.2 μm over a long period of time. However, since this displacement occurs gradually rather than abruptly, correct mask alignment can be performed by knowing the relationship of the IM specific position 0 with respect to the stationary coordinate system at any time and correcting this.

Therefore, in the present invention, a detection mark 11 is newly added on the mask 1.
is provided, and the detection mark 11 can be magnified and observed using a reflecting mirror 12 and an eyepiece [3]. Further, when the wafer 4 is moved from the A position to the B position, the reflected light from the pattern 5 on the wafer 4 is conversely magnified by the reduction lens 3 and formed into an image on the detection mark 11, and the reflection mirror 12 and the eyepiece lens 13 For example, as shown in FIG. 2, an image 14 of a pattern 5 on a medium-sized wafer 4 and an image 15 of a detection mark 1 surrounding it can be detected within the same visual field. . In the following explanation,
When the center of a square pattern such as wafer pattern 5 and the center of a surrounding pattern such as detection mark 11 match, it is defined that both patterns match. Now, if the wafer pattern image 14 and the detection mark image 15 match at position B in FIG. By multiplying by the reduction rate of 3, it is possible to know that 0B=L2. So AB, that is,
It is possible to know AO=LL by measuring the distance that the wafer 5 has been moved after determining the center of the wafer pattern 5 using the microscope optical system until the enlarged image 14 of the wafer pattern matches the detection mark image 15. As a result, mask alignment between the wafer pattern 5 and the circuit pattern 2 on the mask 1 can be performed regardless of the change in the unique position 10.

FIG. 3 is an overhead view showing a detailed embodiment of the present invention.

The wafer 4, on which the positioning pattern 5 has been formed in the pre-processing process, is vacuum-adsorbed onto a movable stage 18 that moves in the X and Y directions by drive mechanisms 16 and 17. The amount of movement of the moving table 18 is measured with an accuracy of 0.1 μm by a length measuring system consisting of a reflection [19° 2o] and a laser interference measuring device 21.

On the other hand, the mask 1 is vacuum-adsorbed by pulse motors 22 and 23 onto a fine movement stage 24 that can move approximately ±50 μm in XY directions, and the center of two vibrating slit photoelectron microscopes 25 and 26 that are fixed relative to the stationary coordinate system. The fine movement table 24 is moved so that the centers of the two mask positioning marks 27 and 28 coincide with the optical axis, and the mask 1 is placed at a fixed position in the stationary coordinate system. Place the pattern of mask 1 on wafer 4.
Objective lenses 29, 30 . 2 consisting of reflectors 31, 32° eyepieces 33, 34 and visual field cross marks 35° 36
A microscope for wafer positioning [1 is provided with an optical system and two wafer positioning marks 37.38 on the wafer 4]
Determine the center position of. The moving table 18 is moved so that the two wafer positioning marks 37 and 38 match the two field cross marks 35 and 36 of the microscope AM optical system, and when they match, the laser measuring device 21 is reset and the XY
Set as the origin of coordinates. After that, the laser interferometric length measuring device 21 is referenced at the predetermined coordinates in order to overlap the circuit pattern 39 on the mask 1 with the circuit pattern (not shown) on the wafer processed in the previous process. The movable table 18 is positioned as follows. When the positioning is completed, the shutter 40 is opened, and the light from the mercury lamp 41 is converted into parallel light by the consonant lens 42 and irradiates the mask 1.

The photoresist on the wafer 4 is exposed through the microlens 3. Thereafter, the movable table 1B is positioned at new coordinates one after another, and exposure is repeated each time. Regarding the positioning of the moving table 18 with respect to the target coordinates, very high precision is not required due to the exposure principle already proposed by the present inventors. That is, if there is a positioning error with respect to the target coordinates of the movable table 18, the control circuit 54
If the fine movement table 24 is moved in the opposite direction by an amount ten times the error according to the command, and used as an exposure optical system, the positioning error is equivalently corrected and the circuit pattern 39 of the mask 1 is placed at the correct position on the wafer 4. to expose.

In the above mechanism, if the two photoelectron microscopes 25 and 26 corresponding to the unique point 10 do not change with respect to the static coordinate system based on the reduction lens 3 and the laser interferometric measurement system, accurate mask alignment is always achieved. However, as mentioned above, since changes occur in reality, it is necessary to calibrate them. During calibration, a mercury lamp 43. condenser lens 4
4. The illumination system consisting of optical fiber 45 is moved to the moving table 1.
8 is inserted into the insertion port 46 provided in the fiber, and the light guided by the fiber is reflected in the reflecting mirror 47. A target mark 49 is illuminated through a condensing lens 48. This target mark 49 is made by a commonly used photomask production process, and a metal chromium film is attached only to the cross pattern portion having a width of 2 μm. On the other hand, a detection mark 50 to be aligned with the target mark 49 is provided at the periphery of the mask 1.
is provided. The position of this detection mark 5o is provided at a position common to all masks with respect to the mask positioning marks 27 and 28. Above the detection mark 50 is a reflecting mirror 51. Objective lens 52. A microscope optical system consisting of an eyepiece lens 53 is provided. Now, while illuminating the target mark 49 with the light guided by the optical fiber 45, move the moving stage 18 so that the target mark 49 is directly below the microscope optical system including the objective lens 29, and The cross mark 29 within the field of view and the image of the target mark 49 are made to coincide. The XY coordinate position of the moving table at this time is read and recorded by the laser interference measuring device 21. Next, the moving stage 18 is moved again so that the target mark 49 is located below the reduction lens 3, and this time the microscope optical system including the objective lens 52 is subjected to IR observation. Since the cross image of the target mark 49 and the detection mark 50 on the mask 1 are detected within the field of view, move the movable table 18 slightly so that they coincide, and determine the xy coordinate position of the movable table 18 when they coincide. Record again.

By the operations described above, the distance of -L2 can be
, we were able to know about the Y axis, and mask 1
Since the distance 2 for each X and Y axis is known from the position of the detection mark 50 on the top, Ll for each X and Y axis can be easily determined. This means that it was possible to calibrate the spatial positional relationship of the mask 1 with respect to the stationary coordinate system that was used as a reference.

In the above embodiment, there is one target laser 1 mark 49, but it is clearly possible to use two marks separated by the distance between the centers of the objective lenses 29 and 30.

However, in this case, the fiber illumination system becomes somewhat complicated.

It is also possible to perform similar calibration without providing these dedicated target marks on the moving table 18 and using a reference wafer on which wafer positioning marks 37 and 38 are formed, but in this case, the illumination of the target marks Naturally, the light becomes reflected illumination through the reduction lens 3, and high target image contrast cannot be obtained, resulting in a disadvantage that the accuracy of matching with the detection mark 50 on the mask 1 is reduced.

As explained above, according to the present invention, the relative positioning of the wafer and mask can be completed once per wafer, and the accuracy of the alignment can be easily confirmed, making it possible to perform highly productive reduction projection exposure. becomes.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of the present invention as well as the operating principle of the conventional device, Fig. 2 is a diagram showing a microscope field image when the wafer pattern and the detection mark on the mask match, and Fig. 3 is a diagram showing the implementation of the present invention. This is an example of an elevation view. 1... Mask, 3... Reduction lens, 4... Wafer, 6... Objective lens, 8... Eyepiece lens, 12...
・Reflector, 13... Eyepiece, 18... Moving table,
54...Control circuit.

Claims (1)

[Claims] 1. When exposing a series of mask figures to a desired position on a photosensitive substrate through a projection lens in an exposure optical system, the series of masks are always placed in the same relative position with respect to the projection lens; The optical relative positioning of the series of masks and the photosensitive substrate is performed by detecting the center of a reference mark provided on the photosensitive substrate by a mark detection optical system fixed outside the optical path of the projection lens. , an exposure apparatus equipped with a magnifying optical system for simultaneously observing a real image of the alignment mark in the focal plane of the projection lens formed on the mask surface by the projection lens and alignment figures of the series of masks; A method for calibrating the spatial positional relationship between an exposure optical system and a mark detection optical system, wherein the center of the alignment mark is detected by the mark detection optical system to determine the optical axis center of the mark detection optical system. find the position of the alignment mark corresponding to the alignment mark, and determine the position of the alignment mark in a state where the alignment mark is moved and the matching of the real image of the alignment mark and the alignment figure is detected by the enlarging optical system. and the alignment mark in a state where the matching between the real image of the alignment mark and the alignment figure is detected by the enlarging optical system based on the distance from the center of the mask to the alignment figure and the magnification of the projection lens. and the center position of the exposure optical system to determine and calibrate the spatial positional relationship between the exposure optical system and the mark detection optical system. Calibration method.