JPH03123016A - Exposing method - Google Patents

Abstract

PURPOSE:To conduct the relative alignment of a mask and a wafer in a highly precise manner by a method wherein an optical image, formed by the reduction lens of the circuit pattern on a mask, is image-formed by accurately superposing it on the pattern on the wafer. CONSTITUTION:A movable stage 18 is shifted in such a manner that a mask 49 is brought to a point directly under a microscope optical system containing an objective lens 29 while a light, which is guided by an optical fiber 45, is being projected on the target mark 49, and the cross mark 35, in the visual field of the microscope optical system, and the image of the mark 49 are brought in coincidence with each other. At this time, the X-Y coordinate position is read out and recorded by a laser interferometer 21. Then, the stage 18 is shifted again in such a manner that the mark 49 comes to the point under a reduction lens 3, and a magnifying optical system, including an objective lens 52, is observed. As the detection mark 5 on the mask 1 can be observed in the visual field together with the image of the mark 49, the stage 18 is slightly moved so as to have the above-mentioned marks brought into coincidence with each other, and the X-Y coordinate position of the stage 18 when they are coincided is recorded again. As a result, the relative alignment of the wafer and the mask is completed by conducting once per wafer, the alignment accuracy can be confirmed easily, and a productive reduced projection and exposure can be conducted.

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. 2. More specifically, the present invention relates to a method for calibrating a projection 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 can be 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 has the advantages of a simple configuration of exposure equipment and the ability to expose the entire wafer at once, making it more productive.However, it is difficult to completely contact the mask to the entire wafer, If a gap is created, a fine circuit pattern cannot be transferred due to light diffraction, and the wafer surface is likely to be damaged when the wafer is brought into close contact with the wafer. 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 1 μm IW pattern has an exposure range at a magnification of 1/10], 4. The limit is around mmφ. Therefore, in order to print a larger wafer, the wafer must be sequentially stepped and exposed several times. In conventional projection exposure equipment, this is done every time the wafer is fed by one step.

The positioning mark on the wafer and the positioning mark on the mask are optically observed through a projection lens, and the mask is normally moved slightly to align the two marks for exposure. 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 coated on the wafer. The device itself, including the switching mechanism, was also complex. IBM Technical Disclos is a projection exposure device that improves the shortcomings of the conventional projection exposure device, that is, a projection exposure device that completes alignment with only one operation for each wafer.
ure Bulletin Volume 13 No. 7 P 18'l
There is a method proposed in 6. In other words, a microscope observation device dedicated to wafer positioning 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 centered within the exposure optical system. The mask and wafer are aligned indirectly. 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 only needs to be positioned once before exposure, which is very productive. However, on the other hand, it is difficult to maintain a constant spatial absolute positional relationship between the microscope device and the exposure optical system for a long period of time. There is a risk of poor relative alignment accuracy between the mask and wafer.

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 X and Y axes. The purpose here is to form an optical image of the circuit pattern 2 of 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. Observe the pattern 5 on the wafer 4 using a microscope optical system (described below as the microscope optical system), and make sure that the pattern 5 coincides with the intersection A of the central optical axis of the microscope optical system and the imaging plane P of the reduction lens 3. Align the wafer 4. On the other hand, if the circuit pattern 2 on the mask 1 is on the central optical axis 1□ of the reduction lens 3, the pattern 5 on the wafer 4 is arranged so that it coincides with the intersection O of the central optical axis 1□ and the plane P. Move the wafer 4, that is, move the wafer 4 by a certain distance A○=L□
By moving the optical image of the circuit pattern 2 by the reduction lens 3, it is possible to match the optical image of the circuit pattern 2 with the pattern 5 on the wafer 4. In this case, the circuit pattern 2 on the mask 1 is positioned i'! on the optical axis 12. [! To do this, a preliminary mask positioning mark 9 is provided on the mask 1, and the mark 9 is placed at a unique position 10 in a stationary coordinate system determined from the microscope optical system and the reduction lens 3. This can be done by matching. However, in actual equipment, the distance between the reduction lens 3 and the mask 1 is approximately 300 to 600 mm, which is a large conical distance, and even if the member that connects them is made of high quality steel, temperature changes and external vibrations may cause the The unique position 1o with respect to the coordinate system changes by about 5 to 0 μm over several days, 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 is not sudden but occurs gradually,
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 enlarged and observed using a reflecting mirror 12 and an eyepiece 13. Furthermore, move the wafer 4 from the A position to the B position.
Then, the reflected light from pattern 5 of wafer/1-1- is 2
The detection mark is magnified inversely by the ih small lens 3]1
An image 14 of a pattern 5 of a medium-sized wafer 4'' is formed and surrounded by an image 14 of a medium-sized wafer 4'', for example, as shown in FIG. An image 15 of the shaped detection mask 11 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 5 and the center of a pattern surrounding it, such as detection mark 1, match, it is defined that both patterns match. Now, whichever wafer pattern image 1.1 and the detection mark image 15 match at position B in FIG.
Since the distance between the two is known, by multiplying the distance by the reduction distance of the reduction lens 3, it is possible to know ○II=L. (8) In other words, after determining the center of the wafer pattern 5 using the microscope optical system, by measuring the distance the wafer 5 has been moved until the enlarged image 14 of the wafer pattern coincides with the detection mark image 15. , A◯=L, thereby making 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 characteristic position [O].

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 .mu.m by a length measuring system consisting of a reflecting mirror 19.degree. 20 and a laser interference measuring device 21.

On the other hand, the mask] is controlled by the pulse motors 22 and 23 to
Two mask positioning marks 27° 28 are placed on the central optical axes of two vibrating slit photoelectron microscopes 25 and 26, which are vacuum-adsorbed onto a fine movement stage 24 that can be moved by about ±50 μm and are fixed relative to the stationary coordinate system. The fine movement table 24 is moved so that the centers of the mask 1 are aligned with each other, and the mask 1 is placed at a fixed position in the stationary coordinate system rNf. Transfer the pattern of master 1 to wafer 4
- Objective lenses 2rr, 3o, reflecting mirrors 31, . ++2
, eyepieces 33, 34 and field of view - 1 character mark 335
Two microscope optical systems consisting of ゜36 are provided and the wafer positioning mark 3 of
Determine the center position of 7389. 2 of this microscope optical system
1 field of view 1- character mark' 5 + 36 vs. 2-
) The movable table 18 is moved so that the wafer positioning marks 37 and 38 of the wafer positioning marks 37 and 38 match, and when they match, the laser measuring device 21 is reset to return to the origin of the XY coordinates. After that, laser interference is applied to the circuit pattern 39 on the wafer processed in the previous process (not shown) at predetermined coordinates to overlap the circuit pattern 39 on the mask].
The movable table 18 is positioned using the long tool 21 as a base. When the positioning is completed, the shutter 40 opens and the mercury lamp 4
The light irradiates the 0 mask 1 with 14 lines of light and the laser beam A using the continuum lens -'+2, and exposes the resist 1 to 1 on the wafer 4 through the reduction lens 3. Thereafter, the movable table 18 is positioned at new coordinates one after another, and exposure is repeated each time. Regarding the positioning of the movable 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, 10 of the error is
If the fine movement table 24 is moved in the opposite direction by twice the amount and used as an exposure optical system, the positioning error is equivalently corrected and the circuit pattern 39 of the mask 1 is exposed at the correct position on the wafer 4.

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.
The target laser 1-mark 49 is illuminated by the light guided by the fiber through the reflecting mirror 47 and the condensing lens 48. This target mark 49 is made by a generally used hole-mask forming 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 cleavage detection mark 50 that matches the target mark 49 is provided on the periphery of the mask 1 . The position of this detection mark 50 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 magnifying 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, the target mark 49 is illuminated by the objective lens 29.
The moving table 18 is moved so as to be directly below the microscope optical system including the microscope optical system, and the image of the cross mark 35 within the field of view of the microscope optical system and the image of the target mark 49 are made to coincide. At this time, the XY coordinate position of the moving table at -11=2 is read and recorded by the laser interference measuring device 21. Next, the moving table 18 is moved again so that the target mark 49 is below the reduction race 3, and this time the magnifying optical system including the objective lens 52 is observed. Since the detection mark 50 on the mask 1 is observed together with the cross image of the target mark 49 within the field of view, the moving table 18 is slightly moved so that they coincide, and the xy coordinate position of the moving table 18 at the time of coincidence is recalculated. Record.

By the operations described above, the distance of L2 is
, 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. With this, the reduction lens 3
And, the spatial positional relationship of the mask 1 with respect to the stationary s41 system based on the laser interferometric measurement system could be calibrated.

Although in the above embodiment there is only one target mark 49, 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 the detection mark 5 on the mask 1 cannot obtain high target image contrast.
There is a drawback that the accuracy of matching with 0 is reduced.

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

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle of the present invention as well as the operating principle of the conventional device, Figure 2 is a diagram showing a microscope field image when the wafer pattern and the detection mark on the mask match, and Figure 3 is a diagram showing the principle of the present invention. FIG. 3 is an overhead track diagram of an embodiment of the invention. 1. Mask, 3. Reduction lens, 4.. Wafer, 6..
Objective lens, 8... Eyepiece, 12... Reflector, 13
- Eyepiece, 18 - Moving table, 54 Control circuit. 5

Claims (1)

[Claims] 1. A step of detecting a mark on a movable table with a mark detection optical system provided off the optical axis of the exposure optical system, and an enlargement optical system including a reduction projection lens of the exposure optical system. a step of detecting a mark on the moving table; a step of positioning the wafer mounted on the moving table at a predetermined position based on the detection results obtained in the above steps of detecting both marks; and a step of exposing the wafer. and an exposure method including. 2. The exposure method according to claim 1, wherein the step of detecting a mark provided outside the optical axis of the exposure optical system with a detection optical system is a step of detecting the mark with a microscope optical system. exposure method. 3. In the exposure method according to claim 2, the step of detecting a mark with the microscope optical system includes a step of detecting a mark on the movable base so that a mark in the field of view of the microscope optical system matches an image of the mark provided on the movable base. An exposure method characterized by comprising a step of reading the position with a laser interferometer measurement system. 4. In the exposure method according to claim 1, the step of detecting the mark on the movable table with the magnifying optical system including the reduction projection lens of the exposure optical system detects the image of the reticle mark within the field of view of the magnifying optical system and the An exposure method comprising the step of reading the position of the movable table using a laser interferometric measurement system so as to match the image of a mark provided on the movable table. 5. The exposure method according to claim 1, wherein the step of positioning the wafer at a predetermined position includes the step of determining the center position of a positioning mark provided on the wafer using the microscope optical system. Method.