JPH03123017A - Exposing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 The present invention relates to a method for calibrating a projection type exposure device that exposes an image with a predetermined positional relationship above a first figure, and more specifically, a projection type exposure device that prints a circuit pattern on a wafer in an integrated circuit manufacturing process. be.

Conventionally, pattern exposure methods used for semi-dedicated quadrature circuits and the like can be broadly classified into two methods: contact exposure method and projection % widening method. The former is a method that has been used since fortune-telling, and has the advantages of a simple exposure equipment configuration and the ability to expose the entire wafer at once, making it more productive. However, it is difficult to bring the mask into complete contact with the entire wafer. Therefore, if a gap is created, a fine circuit pattern cannot be transferred due to the phenomenon of light diffraction, and the wafer surface is likely to be damaged when the wafer is brought into close contact. On the other hand, the latter method has the advantage of not damaging the wafer or even the mask since the wafer 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. Conventional projection exposure equipment optically observes the positioning mark on the wafer and the positioning mark on the mask through a projection lens each time the wafer is fed one step, and usually moves the mask slightly to align the two marks. exposure was carried out. Therefore, it is necessary to perform alignment operations several to several thousand times in order to expose one wafer, making it an unproductive apparatus. In addition, when aligning both 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 1 coated on the wafer. The device itself, including the switching mechanism, was complicated. As a projection exposure apparatus that improves the shortcomings of the conventional projection exposure apparatus, that is, a projection exposure apparatus that completes alignment with only one operation for each wafer, IBM
electrical disclosure bullet
There is a method proposed in TIN Vol. 13, No. 7, P1816. That is, a microscope observation device dedicated to positioning five wafers is provided outside the projection exposure optical system, and after positioning the wafer with respect to the optical axis of this microscope device, the wafer is moved a certain distance and placed inside the exposure optical system. Guide and indirectly align the mask and wafer. Thereafter, the wafer is precisely stepped in XY directions by a certain absolute amount, and exposure is performed to complete the exposure of the entire surface of one wafer. According to this method, the wafer is positioned at 1
However, it is difficult to keep the spatial absolute positional relationship between the microscope device and the exposure optical system constant for a long period of time, and the accuracy of the relative positioning of the mask and wafer is limited. Defects are 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 is possible to perform wafer positioning only once when exposing two wafers, and to provide a mask and wafer that can be stably maintained for a long period of time and have high precision. 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 two XY axes. The purpose here is to form an optical image of the circuit pattern 2 on the mask 1 by the reduction lens 3 so as to accurately overlap the pattern 5 on the wafer 4. In the conventional apparatus, a mark detection optical system, for example, a microscope optical system, includes an objective lens 6, a reflector 7, an eyepiece 8, and an epi-illumination system (not shown), which are firmly fixed to the reduction lens 3. The pattern 5 on the wafer 4 is observed using a microscope optical system (described below as the microscope optical system), and the wafer is moved so that the pattern 5 coincides with the intersection A of the central optical axis 11 of the microscope optical system and the imaging plane P of the reduction lens 3. Align 4. On the other hand, if the circuit pattern 2 on the mask 1 is on the central optical axis 12 of the reduction lens 3, the wafer 4 is located at the intersection O of the central optical axis 1□ and the plane P.
By moving the wafer 4 so that the patterns 5 on the wafer 4 match, that is, by moving the wafer 4 by a certain distance AO2L, the optical image of the circuit pattern 2 by the reduction lens 3 is converted into the pattern 5 on the wafer 4. can be matched. In this case, in order to arrange the circuit pattern 2 on the mask 1 on the optical axis 12, a mask positioning mark 9 is provided on the mask 1 in advance, and the positioning mark 9 is determined from the microscope optical system and the reduction lens 3. This can be done by aligning the mark 9 with a unique position 10 on a stationary coordinate system. However, in actual equipment, the distance between the reduction lens 3 and the mask 1 is 300 to 600 m.
Even if the members that connect them are manufactured with high steel quality, due to temperature changes, external vibrations, etc., the characteristic position 10 with respect to the stationary coordinate system will change over a few days. It changed by about 1071m, and the temperature ranged from 0.1 to 0 over a long period of time.
．． It is difficult to perform mask alignment with an accuracy of 2 μm.

However, since this displacement occurs gradually rather than abruptly, correct mask alignment can be performed by knowing the relationship of the unique position 10 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 1] 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 reflected by the reducing lens 3.
The image is conversely magnified and formed onto the detection mark 11 by a magnifying observation system consisting of the reflector 12 and the eyepiece 13.

For example, as shown in FIG. 2, an image 15 of a pattern 5 on a medium-sized wafer 4 and a detection mark 1 surrounding it can be observed within the same field of view. In the following description, when the center of a medium-sized pattern such as wafer pattern 5Φ and the center of a pattern surrounding it, 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. 0 by multiplying the reduction rate of reduction lens 3
It is possible to know that B=L2. Therefore, AB, that is, by measuring the distance traveled by the wafer 5 after determining the center of the wafer pattern 5 using the microscope optical system until the enlarged image 14 of the wafer pattern coincides with the detection mark image 15, A○=L1 This makes it possible to perform mask alignment between the wafer pattern 5 and the circuit pattern 2 on the mask 1 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 table 18 that moves in x and y directions by moving mechanisms 16 and 17. The amount of movement of the moving table 18 is measured with an accuracy of 0.1 .mu.In by a length measuring system consisting of a reflecting mirror 9.degree. 20, a laser interference 41, and a measuring device 21.

-・Kamasuf] are vacuum-adsorbed by a pulse motor 22.23 to a fine movement table 2=11 that can move about ±50 μm in XY directions, and are fixed to the stationary coordinate system using two vibrating Surino I~ type photoelectric microscopes 25. The fine movement table 24 is moved so that the centers of the two mask positioning marks 27 and 28 are aligned with the center optical axis of the mask 1, and the mask 1 is placed at a fixed position in the stationary coordinate system. 3. Pattern of the mask 1 Objective lenses 29, 30, reflecting mirrors 31, 32,
Eyepiece lens 33.34 and visual field cross mark 35°36
Two microscope optical systems consisting of
Determine the center position of the upper two wafer positioning marks 37° and 38. The two wafer positioning marks 37 are connected to the two field cross marks 35 and 36 of this microscope optical system.
．． 38 are aligned, and when they are aligned, the laser measuring device 21 is reset and set as the origin of the XY coordinates. (+) After that, laser interferometry is carried out at the predetermined coordinates to overlap the circuit pattern 39 on the mask 1 on the circuit pattern (not shown in the figure) on the wafer processed in the previous process. The movable table 18 is positioned with respect to the container 21. 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 condenser lens 42 and irradiates the mask 1. The resist on the wafer 4 is exposed. After that, the moving table 18 is positioned at new coordinates one after another, and the exposure is repeated each time. Regarding the positioning of the moving table 18 with respect to the target coordinates, According to the exposure principle already proposed by the present inventors, very high accuracy is not required.In other words, if there is a positioning error of the movable table 18 with respect to the target coordinates, the amount of the error is ten times that error according to the command of the control circuit 54. When the fine movement table 24 is moved in the opposite direction by the same amount as the exposure optical system, the positioning error is equivalently corrected and the circuit pattern 3 of the mask 1 is placed in the correct position on the wafer 4.
Expose 9.

In a mechanism with more than one lens, the two photoelectron microscopes 25 and 26 corresponding to the characteristic point 10 must be fixed with respect to the static coordinate system with the reduction lens 3 and the laser interferometric measuring system as the base 7 (Q). Accurate mask alignment is always performed, but as mentioned above, changes occur in reality, so calibration is necessary.During calibration, the illumination system consisting of a mercury lamp 43, a condenser lens 44, and an optical fiber 45 is moved. The target mark 49 is inserted into the insertion opening 46 provided in the table 18, and the target mark 49 is illuminated by the light guided by the fiber through the reflecting mirror 47 and the condensing lens 48. A metal chromium film is attached only to the cross pattern portion having a width of 2 μm.On the other hand, a crevice detection mark 50 is provided on the periphery of the mask 1 to match the target mark 49. The detection mark 5o is provided at a position common to all masks with respect to the mask positioning marks 27 and 28. On one side of the detection mark 50 is a magnifying optical system consisting of a reflecting mirror 51, an objective lens 52, and an eyepiece lens 53. Now, the target mark 49 is brought directly under the microscope optical system including the objective lens 29 while illuminating the target marks 1 to 49 with the light guided from the buttical fiber 45. Like moving platform 1
8 to match the cross mark 35 within the field of view of the microscope optical system with the image of the target mark 49. 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 below the reduction radar 3, and this time the magnifying optical system including the objective lens 52 is observed. Mask 1 is in the field of view along with the crosses of Tagera 1 to Mark 49.
Since the upper detection mark 50 is observed, move the moving table 18 slightly so that these marks match, and when they match, the moving table 1
Record the xy coordinate position of 8 again.

By the operations described above, the distances L1 and L2 described above are
, we were able to know about the Y axis, and mask 1
Since L2 for each of the X and Y axes is known from the position of the detection mark 50 above, Ll for each of the X and Y axes can be easily determined.

This makes it possible to calibrate the spatial positional relationship of the mask 1 with respect to the stationary coordinate system based on the reduction lens 3 and the laser interferometric measurement system.

In the above embodiment, there is one mark 49 on the target solenoid 1, 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 the wafer 1 positioning marks 37 and 38 are formed, but in this case, the target marks Naturally, the illumination 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 the mask can be completed once for each wafer, and the accuracy of the alignment can be easily confirmed, making it possible to perform highly productive reduction projection exposure. becomes possible.

[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 the example of withdrawing the head. 1. Mask, 3. Reduction lens, 4. Wafer, 6.
...Objective lens, 8.Eyepiece lens, 12.Reflector,
13... Eyepiece lens, 18... Moving table, 54... Control circuit. 3 4 JP-A-3 123017 (5)

Claims (1)

[Claims] 1. Exposure comprising a reticle, an exposure optical system means for transferring a pattern on the reticle onto a wafer, a movable table for mounting the wafer, and a detection means for detecting the position of the wafer. A reduction projection exposure apparatus characterized in that a mark detected by the detection means is provided on the movable table. 2. The reduction projection exposure apparatus according to claim 1, wherein the mark provided on the movable table is in the shape of a cross. 3. The reduction projection exposure apparatus according to claim 1, wherein the mark provided on the movable table is formed from a metal chromium film. 4. The reduction projection exposure apparatus according to claim 1, wherein the mark provided on the movable table is provided on a light transmitting plate.