JPH0799731B2 - Alignment device - Google Patents

Description

Description: 1) Field of the Invention The present invention relates to an apparatus for printing a fine pattern on a semiconductor wafer, in which the mutual positions of a pattern already printed on the wafer and a new pattern to be printed are set. It relates to a device for accurate alignment.

2) Description of prior art Semiconductors such as ICs and LSIs are completed by baking extremely fine patterns on a silicon wafer several times. When printing such fine patterns over and over again, the second and subsequent bakings must be performed the next time after the previously baked pattern. Has become a very important issue.

Conventionally, as an example of means for performing such alignment, the method shown in FIGS. 1, 2, and 3 has been considered. That is, at the time of the previous pattern printing, a target for aligning the next pattern is simultaneously baked in advance in a vacant area on the wafer (for example, on a part which becomes a cutting line) in advance, and the next pattern printing is performed. Is
This is done by aligning the target of the next pattern (which is normally created on the mask at the same time as the next pattern) exactly to the position of the target that was previously burned. FIG. 1 is an example of such a pattern, 3 is a target on the wafer that is baked on the wafer at the same time as the previous pattern, and 1 is a target on the mask that is made on the mask at the same time as the next pattern. Is. Further, 2 shows a part of the mask, and 4 shows a part of the wafer. Reference numeral 5 is an optical axis of an optical system for observing the positions of the target on the mask and the target on the wafer. (In FIG. 1, an optical system for observation is not shown and only an optical axis is shown.) FIG. 2 shows an example in which the target on the mask and the target on the wafer are simultaneously observed through the observation system. 6 is a target on the mask, and 7 is a target on the wafer. Here, each target is made so that the pattern on the previous wafer and the pattern on the next mask match when the target on the wafer is exactly aligned with the center of the target on the mask. FIG. 3 shows a part of such an optical system for observing a target and an optical system for printing an IC pattern. 18 is an IC pattern for next printing,
It is printed on the previous IC pattern 13 through the reduction projection lens 14. Reference numeral 17 is a transparent member that holds the pattern 18, and usually 17 and 18 are collectively called a mask. 11 is a silicon wafer which is a material for making an IC, and all patterns are printed on this. 32 is what is commonly called an XY stage for moving the silicon wafer 11 with extremely high precision.In this case, the wafer is positioned in a plane perpendicular to the baking optical axis 15, and the direction indicated by the arrow 33. It is also movable. The purpose of moving in the direction of arrow 33 is
It is the mechanism required to focus the image of the pattern 18 on the mask onto the surface of the wafer 11. Although the IC pattern 18 is printed by a positioning mechanism, the previous pattern and the next pattern are matched, and although not shown in the drawing, after focusing by a separately existing focusing mechanism, a powerful printing pattern is indicated from 34. Irradiate light and pattern on the mask
18 is projected through a reduction projection lens 14 to a predetermined position on the wafer. Next, the position lowering mechanism will be described. (In this case, the alignment target is assumed to be the one shown in FIG. 1) The light emitted from the target illumination lamp 25 travels along the optical axis 30,
Only the necessary wavelength components are collected by the lens 26 and extracted through the filter 27. After that, the light is reflected by the semi-transmissive prism 23, passes through the optical axis 31, the prism 22, the optical axis 28, the observation optical lens 21, the mirror 20, the optical axis 16, and the reduction projection lens 14, and irradiates the target 12 on the wafer. The light reflected by the target 12 follows the current path in reverse, passes through the semi-transparent prism 23,
It reaches the TV camera 24 via the optical axis 29. In addition, a part of the light that illuminates the target on the wafer is reflected at the peripheral part of the target on the (peripheral part) mask, and the TV camera also
Come back to 24. Here, in order to simultaneously observe the target 19 on the mask and the target 12 on the wafer with the TV camera 24, the image of the target 12 on the wafer is back-projected to the position of the target 19 on the mask by the projection lens 14. The focus position at the time of exposure must be in the same plane as the target on the mask.

3) Problems of the prior art As described in the section of the prior art, in order to perform accurate alignment between the mask pattern and the wafer pattern, images of both the target on the mask and the target on the wafer are displayed on the TV camera. You have to focus on. If the light for printing the pattern and the light for observing the alignment target have the same wavelength, the target is also in focus when the pattern is in focus, so if the device shown in FIG. 3 is used, The target on the mask and the target on the wafer can be simultaneously observed with a television camera. However, in this case, the target illuminating light exposes the photosensitive material on the wafer during the observation of the alignment target that must be performed before printing. For this reason, measures such as using an ultra-high-sensitivity TV camera and weakening the illumination light have been taken, but this is not perfect. Further, when using light of the same wavelength as the baking light, there is a more important problem. Generally, the pattern forming sensitizer is made to have good sensitivity at the wavelength of the printing light. The photosensitizer is applied over the entire surface of the wafer, and of course is applied over the target on the wafer. That is, the target on the wafer is observed through this sensitizer,
When observed with light having a wavelength with a good sensitivity of the photosensitizer, most of the irradiation light is absorbed, and the light that reaches the target on the wafer and is reflected and returned becomes extremely small. In this way, if you try to observe the target on the wafer with the same light as the baking light, the target body can hardly be seen, and only the unevenness generated on the surface of the photosensitive agent by the target will be observed, This has a significant adverse effect on alignment.

Next, a system in which the wavelength of the light for irradiating the target on the wafer and the wavelength of the light for printing are made different is also in practical use. In this case, since the photosensitizer has almost no sensitivity to the light irradiating the target, it is possible to observe the target on the wafer through the film of the photosensitizer. Further, even if a sufficiently strong light is irradiated, the target portion is not exposed. However, since the reduction projection lens is an advanced lens that pursues the limit of lens technology, various errors are generally corrected only for the wavelength of light for printing. When observing a target on a wafer through such a lens, when observing with a light having a wavelength different from the light for printing, the focus position of the printing light and the focus position of the target observation light usually differ. As a means for correcting such a phenomenon, a method is adopted in which the XY stage is slightly moved in the direction indicated by the arrow 33 in FIG. 3 so that the focus is adjusted during positioning and printing. Since such a means involves mechanical movement between the time of positioning and the time of baking, many errors are introduced. Also,
Although a reduction projection lens is designed and manufactured so that the focal positions of printing light and observation light are the same, such means adversely affect the performance of the reduction projection lens itself.

4) Object of the Invention It is an object of the present invention to provide an alignment apparatus capable of improving the accuracy of reading the positions of the target on the mask and the target on the wafer and performing the alignment between the targets more accurately. is there.

5) Features of the Invention The present invention is an apparatus for aligning a target provided on a wafer with a target serving as a reference for alignment, and a first target provided at a predetermined position on the wafer. And a first light source for irradiating the first target with light having a predetermined narrow band wavelength, and the first light source at a predetermined distance from the surface of the wafer on which the first target is provided. A second target disposed on the side, a second light source for irradiating the second target with light having a predetermined narrow band wavelength different from the first light source, and the first target. An observation lens provided so that the first target irradiated with the light of the different wavelength and the focal positions corresponding to the second target coincide with each other while observing the second target together; One light source and a shutter provided in front of the second light source, and an observation provided so as to observe an image formed at the common focus position by individually opening and closing the shutter at different times. It is characterized by comprising means and means for storing the data of this observation means.

6) Embodiment FIG. 4 shows an embodiment of the present invention. The basic structure is the third
Although similar to the prior art shown in the figure, the part related to irradiation of the target and the lens system for observing the target are completely different. In the figure, 47 and 48 are a mask and an IC pattern to be printed next time, and 49 is a target on the mask side. The target is the same as that shown in FIGS. 1 and 2. 44 is a reduction projection lens, 43 is an IC pattern on the wafer, and 42 is a target on the wafer side. As in the case of FIG. 3, the IC pattern on the mask 47 is reduced and projected onto the wafer by the strong printing light emitted from above the mask, and the photosensitive agent coated on the wafer is exposed. Next, a method of alignment will be described. When the condensation projection lens is in focus with respect to the wavelength of the baking light, when the target 42 on the wafer is irradiated with light having a wavelength different from the wavelength of the baking light, the reduction projection lens 44 causes the mask 47 to move. The real image of the target on the back-projected towards the wafer can be located at 52. Generally, the reduction projection lens is designed to eliminate various errors only in the printing light, so at the position where the printing light focuses, the real image of the target on the wafer formed on the mask side 1C pattern 48 on the mask or target 49 on the mask as shown at 52
Can be a different plane than. Therefore, even if this is observed through an ordinary lens, the image of the target 49 on the mask and the real image of the target at the position of 52 on the wafer cannot be simultaneously focused on the television camera 55 through the observation lens 53. As a means for observing images with different focal positions at the same time, there is a bifocal lens that utilizes birefringence of a special crystal. However, the bifocal lens of this type has many restrictions in design, and it is very difficult to make an observation lens having two desired focal positions.

The present invention intends to match the image of the target on the wafer and the image of the target on the mask at different focal positions at the same time on the television camera by devising a normal lens achromatic technology and the irradiation light of the target. Is.

Here, returning to FIG. 4 again, the description will be continued. 65, 66, 67 in the figure
Is a light projecting portion for illuminating the target on the wafer, and irradiates the target on the wafer with light in the vicinity of 500 nm, for example. Further, reference numerals 68, 69, and 70 denote light projecting portions for irradiating the target on the mask, for example, irradiating light near 600 nm toward the target on the mask. These two kinds of light are combined by the semi-transmissive prism 64 and irradiate both targets at the same time, but there is no particular problem. Next, the observation lens 53 is provided on the TV camera and in the figure with respect to the light irradiating the target on the wafer (light of 500 nm in the previous example).
It is designed so that the light is focused at the position indicated by and the light irradiating the mask (light of 600 nm in the previous example) is focused on the TV camera and at the position indicated by 51 in the figure. As described above, it is relatively easy to design and manufacture a lens having a different focal position for lights having different wavelengths, and the lens can be freely designed only by giving a wavelength and a focal position of the light. . The procedure for manufacturing the alignment apparatus according to the method of the present invention is as follows.

i) Wavelength of light (for example, 250 nm) for printing a reduction projection lens
Focusing only on this, design and manufacture with the best technology.

ii) Know the focal position when the wafer target illumination light (for example, 500 nm) is passed through the reduction projection lens obtained as a result of the above design.

iii) Determine the wavelength of the light that illuminates the target on the mask. (Eg 600 nm) iv) When the difference between the focal position when passing the baking light through the reduction projection lens and the focal position when passing the light illuminating the target on the wafer, the observation lens is It is designed so that the difference between the focal position of the irradiating light and the focal position of the irradiating light on the target on the mask is the same.

7) Other application examples of the invention The gist of the present invention is to irradiate a target on a wafer and a target on a mask with lights having different wavelengths, respectively, to thereby create a printing pattern generated by a reduction projection lens and a target for alignment. It is to correct the shift of the focal position, and various application examples can be considered. In the embodiment of FIG. 4, light having two kinds of wavelengths for irradiating both targets is combined and irradiated, but the light for irradiating the target on the wafer is directly irradiated onto the wafer without passing through the reduction projection lens. It is also possible to illuminate and return only the reflected light from the target to the television camera through the reduction projection lens. Further, the light for irradiating the target on the mask can also irradiate the target on the mask from between the mask and the reduction projection lens, and only the image of the target on the mask can be maximized. Furthermore, each light source for irradiating the target is provided with a shutter, first irradiates only the target on the mask, and the control unit stores only the image data of the target on the mask, and subsequently irradiates only the target on the wafer. By doing so, the position of the target on the wafer can also be read. Also, since there is no need to move the XY stage between alignment and exposure, the exposure is divided into several times (this happens when the printing light is obtained from a pulsed laser). You can also check. Further, in the above description, there was a reduction projection lens between the mask and the wafer, but when the baking light became X-ray, such a lens disappeared, and the distance between the mask and the wafer was several microns to several tens of microns. It is placed and placed. However, even in this case,
By applying the configuration of the present invention, it is possible to simultaneously observe the target on the wafer and the target on the mask with a television camera.

8) Effects of the Invention According to the present invention, for example, the target on the wafer and the target on the mask can be observed at the same time without mechanical movement of the alignment optical system, and exposure can be performed at the same time. . In recent years, miniaturization of semiconductor circuit patterns has advanced, and a shift of 0.01 micron has been discussed in terms of alignment. When attempting to realize such minute alignment and printing, if there is a mechanical offset between the measurement position for printing and the printing position, this offset is corrected by the laser side length device. However, an error will occur. When measuring a displacement of 0.01 micron with a laser length measuring machine, such an error easily occurs due to a slight fluctuation of air in the optical path along which the measuring light is running. Therefore, when discussing the positioning of 0.01 micron, it is important to perform the alignment at the printing location itself.After the alignment, during the exposure, the static servo of the XY stage uses air fluctuations. Considering the adverse effects caused by, it is preferable not to use a laser length measuring device. According to the alignment method of the present invention, when the alignment is performed at the above-mentioned printing location itself, the static servo of the XY stage can be operated without using a laser length measuring device, for example, by using a glass scale or the like. Both of these are possible and will bring great advances to the technology for overprinting fine IC patterns.

Further, in the present invention, the shutters are provided in front of the first and second light sources for irradiating the first and second targets with lights having different wavelengths, respectively. Only the image data of the target on the mask is stored in, for example, the controller as a means for storing the data, and then only the second target, for example, the target on the wafer is irradiated. By irradiating the light from the second light source, the image data of the target on the wafer can be read. Therefore, the accuracy of reading the positions of the first target and the second target can be improved, and the alignment between the targets can be performed more accurately. In particular, when observing the first target and the second target at the same time, it is effective for aligning the targets that are difficult to observe and may cause erroneous detection.

[Brief description of drawings]

FIG. 1 is a view showing an example of a positioning target used in the present invention and the prior art, FIG. 2 is a view of the target seen through an observation device, and FIG. 3 is a view showing an example of the prior art. FIG. 4 is a diagram showing an embodiment of the alignment apparatus according to the present invention. In the figure, 1 ... A target for alignment provided on the mask, 2 ... A part of the mask member, 3 ... Target for alignment provided on the wafer, 4 ...
… Part of wafer, 5 …… Optical axis of optical system for observing both targets, 6 …… Target on mask, 7 …… Target on wafer, 11 …… Wafer, 12 …… Target on wafer, 13 …… IC pattern on wafer, 14
...... Reduction projection lens, 15 …… Optical axis of printing optical system, 16…
… Optical axis of alignment optical system, 17 …… Mask plate, 18 …… IC pattern drawn on mask, 19 …… Target for alignment made at the same time as IC pattern, 20 …… Reflecting prism, 21… … Magnifying lens for observing the target, 22 ……
Reflective prism, 23 …… Semi-transmissive prism, 24 …… TV camera, 25 …… Illumination lamp, 26 …… Lens composing illumination optical system, 27 …… Wavelength selection filter, 28 …… Optical axis of target observation system , 29 …… Optical axis of the target observation system, 30 ……
Optical axis of target illumination system, 31 …… Optical axis of target observation system, 32 …… XY stage that moves wafer, 34 …… Baking light, 41 …… Wafer, 42 …… Target on wafer (second target ), 43 ... IC pattern on wafer, 44 ... Reduction projection lens, 45 ... Optical axis of baking optical system, 46 ... Optical axis of alignment optical system, 47 ... Mask plate,
48 …… IC pattern drawn on the mask, 49 …… Target for alignment (first target) drawn on the mask,
50 …… Focal position with printing light of reduction projection lens, 51 ……
Focus position in light illuminating target on mask of target observation lens, 52 ... Focus position in light illuminating target on wafer of target observation lens, and target on wafer of reduction projection lens Focusing position with light, 53 ... Target observation lens whose focal position changes depending on the wavelength of light, 54 ... Semi-transparent prism, 55 ...
… TV camera, 56 …… Baking light, 57 …… Reflected light from target on wafer, 58 …… Reflected light from target on wafer, 59 …… Reflected light from target on mask, 60 …… Mask Focus position of observation lens for upper target illumination light, 61 ... Focus position of reduction projection lens for printing light, 62 ... Focus position of observation lens for target illumination light on wafer, 63 ... Target illumination light on wafer The focal position of the reduction projection lens with respect to 64
...... Semi-transmissive prism, 65 …… Wavelength selection filter, 66 …… Illumination system lens, 67 …… Illumination lamp (second light source), 68 ……
... wavelength selection filter, 69 ... illumination system lens, 70 ... illumination lamp (first light source).

Claims (1)

[Claims] 1. An apparatus for aligning a target provided on a wafer with a target serving as a reference for alignment, comprising: a first target provided at a predetermined position on the wafer; A first light source for irradiating a first target with light having a predetermined narrow band wavelength and a surface of the wafer on which the first target is provided are arranged on the first light source side at a predetermined distance. A second target, a second light source for irradiating the second target with light having a predetermined narrow band wavelength different from the first light source, the first target and the second target. An observation lens provided so that the focal positions corresponding to the first target and the second target, which are irradiated with the light of the different wavelengths, coincide with each other, and the first light source and the observation lens. A shutter provided in front of the second light source, an observation unit provided to observe the image formed at the common focus position by individually opening and closing the shutter at different times, and A positioning device comprising: a means for storing data of an observing means.