JPS6212657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray exposure apparatus in the field of X-ray phosphorography capable of copying fine patterns of 1 micron or less.

Publication Electronics Published in 1972
Letters (ELECTRONICS LETTERS) No. 8
Since the report on copying high-resolution patterns using soft X-rays in Vol. 4, pp. 102-104, research and development on X-ray phosphorography has been actively carried out in various places. An outline of this prior art is shown in FIG. For example, the publication IEEE TRANSACTIONS on Electron Devices published in 1975
ON ELECTRON DEVICES), Vol. ED-22, No. 7, pp. 429-433, or in Patent Application Publication No. 41511 of 1976, a similar diagram is published on the method and apparatus for soft X-ray lithography. It's on. Electron beam 12 to fixed or rotating metal target 11
For example, soft X-rays 13 excited downward strike a sample consisting of a mask 14 and a substrate (wafer) 15 coated with resist and copy the pattern on the mask onto the substrate. A tube section 16 with a high vacuum of about 10 ^-6 Torr and a sample chamber 17 with a low vacuum of about 10 ^-2 Torr or about 1 atm of He gas with low attenuation of soft X-rays are separated by a window section 18 . 19 indicates high vacuum evacuation of the tube section, and 20 indicates low vacuum evacuation or He gas replacement of the sample chamber.

In X-ray lithography, (1) the number of wavelengths used is
Because it is a so-called soft X-ray region of several tens of angstroms, there is essentially no problem of diffraction or reflection, and 1
Suitable for creating fine patterns below microns
(2) Since X-rays pass through dirt and dust on the mask or substrate, there is no effect from these. (3) As an X-ray exposure system, it is structurally simple and relatively easy to use compared to electron beam exposure systems. It has characteristics such as being inexpensive. As described above, it has various advantages and is highly anticipated as a copying technology, especially in the submicron region. However, the current state of research and development as an X-ray exposure device is still somewhat sluggish. In particular, a simple X-ray exposure apparatus that is easy to handle and that reliably guarantees copying in the submicron region has not yet been commercially available. One important factor in this regard is the difficulty in effectively combining or integrating the x-ray source and alignment sections. Next, this point will be explained using three specific conventional examples. The publication Proceedings International Conference on Microlithography (PROC.INT.CONF.ON) published in 1977
MICROLITHOGAPHY), pp. 195-199, an X-ray exposure device was proposed and announced by Bell Laboratories in the United States. The feature of this equipment is that during X-ray exposure, the stage section carrying the sample consisting of a mask and wafer aligned by an optical alignment section with a bifocal lens moves linearly to below the radiation source section for exposure. At the point. In other words, alignment and exposure are performed in separate locations, and a series of steps are performed by linearly moving a stage on which a mask and a wafer are mounted. A second example is the 1978 publication Journal of Bacijuum Science and
Technology (J.VAC.SCI.TECHNOL.), No. 15
Volume, No. 3, pages 974 to 976, an X-ray exposure apparatus is proposed and announced by GI (GENERAL INSTRUMENT) of the United States. The feature of this device is that the alignment part is a commercially available Cobilt.
2020 aligner is used, and after optical alignment is completed, the radiation source is moved horizontally onto the aligned sample with the head of the aligner raised and exposed. That is, the stage on which the mask and wafer are mounted remains fixed to the aligner, and the radiation source moves linearly. As a third example, in the publication SOLID STATE TECHNOLOGY published in August 1979, pages 95 to 100, an X-ray exposure device was proposed and announced by Hughes Corporation of the United States. . The feature of this device is that a commercially available co-built aligner is used as the alignment part, and after optical alignment is completed, the radiation source part is moved approximately with the head part of the aligner raised.
It is at the point where it moves to the aligned sample by oscillating around 90 degrees and exposes it. In other words, the stage carrying the mask and wafer remains fixed to the aligner, while the radiation source rotates approximately 90 degrees.

The typical relatively simple X-ray exposure apparatuses that have been prototyped and developed so far have been described above, but they all have the following common drawbacks. (1) Linear or rotational movement of the radiation source section or the stage section on which the mask and wafer are mounted is included in a series of steps, and it is especially difficult to integrate it into a commercially available device compared to a normal light exposure device. (2) An optical aligner is used as the alignment part, and the inclusion of a moving part in the device greatly impairs the reliability of copying submicron patterns.
This is insufficient for alignment in submicron pattern copying.

Therefore, an object of the present invention is to consider a simple type of X-ray exposure apparatus suitable for practical use and commercial use, which can reliably guarantee copying in the submicron region in particular, and to propose an effective alignment method that is most important in this case.

A feature of the present invention is that in an X-ray exposure apparatus equipped with an X-ray source section, a stage section carrying a mask and a wafer, and an alignment section 5, these main sections are fixed during a series of exposure steps, and It has an alignment system, uses the transmitted total X-ray dose as the alignment mark for calibration, and uses an asymmetric metrological pattern that does not match even when a pair of alignment marks are moved in parallel.

Next, the configuration of the present invention will be explained in detail using figures and the like.

Alignment using X-ray flux itself was proposed in the article in which X-ray phosphorography was proposed, and for example, in the 1973 publication Journal of Bacilum Science and Science.
Technology (J.VAC.SCI.TECHNOL.), No. 10
Volume, No. 6, pages 913-917 contain diagrams of the basic principles. FIG. 2 shows this schematic diagram. mask 2
There is an alignment mark 24 on the wafer 23 corresponding to the alignment mark 22 on the wafer 1 . A state of good alignment can be determined when the amount of X-rays that enters from above the mask, passes through the wafer, and enters the left and right X-ray detectors 25 becomes almost zero. Alignment experiments using X-ray beams were extensively carried out by Hughes Corporation, but were found to have the following serious drawbacks. Publication Proceedings of the Symposium on Electron and Ion Beam Science and Technology published in 1976
ELECTRON AND ION BEAM SCIENCE
AND TECHNOLCGY, pp. 536-544, or the publication SOLID STATE TECHNOLOGY, also published in 1976.
The circumstances are described in detail in the September issue of TECHNOLOGY, pages 59-64. In short, because the contrast between the alignment marks on the mask and the wafer is insufficient, a considerable amount of X-rays passing through the marks themselves become noise, resulting in a significant deterioration of the S/N ratio in alignment. This is due to the fact that technically it is extremely difficult to create absorber patterns with high resolution and thick enough to stop the X-ray flux. 1978
Publications published in 2013CIRCUITS
MANUFACTURING, January issue, pages 30-40, IBM's GAWardly5 makes the following pessimistic view regarding X-ray alignment. If alignment marks were created using existing electron beam exposure devices, it would be impossible to require higher absolute positional accuracy than that of these lithography devices themselves. When considering submicron copying, an alignment accuracy of 0.1 micron or less is required, which is difficult to achieve with the above-mentioned drawing equipment.
It is currently impossible to require dimensional accuracy of 0.1 micron or less. From this point of view, one cannot help but be somewhat pessimistic about alignment technology using X-rays.

The problem with X-ray alignment technology is that the alignment marks on the mask and wafer cannot be made thick enough to provide high resolution and sufficient contrast, and the absolute dimensional accuracy of the alignment marks, especially the correlation between the mask pattern and the wafer pattern, is a problem. As mentioned above, it is not possible to guarantee absolute position accuracy as required.

The present invention is a proposal for solving these problems.

One embodiment according to the invention is shown in FIG. FIG. 3a shows a state in which the alignment is completed. For example, the alignment mark 31 on the mask made of an Au absorber pattern and the alignment mark 32 on the wafer of the same shape completely overlap, and the mark 31' on the right side , 32' are also the same. X-rays incident from above the mask pass through the transmission area 100 and are calibrated by an X-ray dose detector installed below the wafer. In Figure 3a, the mark on the mask and the mark on the wafer tend to overlap, so the mark 3 on the wafer that limits the amount of transmitted X-rays
The entire area 100 defined by 2 is a transmission area. The transmitted X-rays are similarly calibrated under the mark on the right side, and the alignment state is determined based on the balance of the total X-ray doses calibrated by the left and right X-ray dose detectors. In Figure 3a, the total X-ray dose on the left and right sides is equal. FIG. 3b shows a case where the mask is slightly shifted to the right with respect to the wafer. Based on the misalignment between mark 33 on the left mask and mark 34 on the wafer, the X-ray transmission area under the left mark is 101
, and the total amount of X-rays passing through region 101 is calibrated. From the degree of deviation between the mark 33' on the right mask and the mark 34' on the wafer, the total amount of X-rays passing through the region 101' under the right mark is calibrated. As is clear from FIG. 3b, the area 101 on the left side and the area 101' on the right side are clearly different in area, resulting in a difference in the total X-ray doses calibrated respectively. This difference is fed back to the mask and wafer drive systems so that the detected X-ray doses are equal to each other. Alignment is possible in this way. What is important here is that the total amount of X-rays passing through the transmission area is calibrated. If such a method of calibrating the total amount of transmitted X-rays is adopted, high resolution and sufficiently thick alignment marks on the mask and wafer are no longer required. In other words, according to the principle of alignment using this method, the transmission of X-rays under the alignment mark is not inherently inconvenient, so there is no need for a very thick alignment mark, and since the difference in the transmission area is important, it is not necessarily necessary to use high resolution. It does not have to be an alignment mark. Furthermore, for the same reason, the requirements regarding the absolute dimensional accuracy of the alignment mark need not be so strict. Therefore, the present scheme is relatively easily achievable by conventional techniques and eliminates the conventional problems.
However, any alignment mark is not sufficient to achieve this method. That is, the third
As shown in the figure, each alignment mark is an asymmetrical pattern that does not match exactly even if the left and right alignment marks are moved in parallel and overlapped, and is a metric pattern in order to utilize the total amount of transmitted X-rays for detection. Must. In Figure 3, there is a double semicircular concentric pattern, but this can be multiple, and in order to detect the X-ray dose, a pattern with a certain area is called a metric pattern. There must be. However, as is clear from Figure 3, the pattern shown can only achieve horizontal alignment.
Other vertical alignment marks are required for vertical alignment.

The effects of the present invention will be described. First, according to the present invention, X
Alignment using a beam bundle becomes easily possible, and copying technology in the submicron region can be made practical. Second, the X-ray exposure apparatus of the present invention guarantees more reliable submicron copying because the X-ray source section, the stage section on which the mask and wafer are mounted, and the alignment section are fixed during a series of exposure steps. do. Thirdly, when the alignment using the X-ray flux of the present invention is adopted, it is easy to use the X-ray flux from the exposure X-ray source as the X-ray flux, and it is possible to realize a simple and widespread type of X-ray exposure apparatus for practical use. It becomes possible.

FIG. 4 shows another embodiment of the invention. As shown in the figure, a combination of rectangles of different lengths are used as alignment marks on the mask and wafer. FIG. 4a shows a state in which the alignment is completed, and the alignment mark 41 on the mask and the alignment mark 42 on the wafer completely overlap, and the same is true for the marks 41' and 42' on the right side. At this time, the X-ray transmission areas 200 and 2 under the left and right marks
The areas of 00' are equal. If the mask is slightly shifted to the right with respect to the wafer, the X-ray transmission areas 201, 201' under the left and right marks as shown in Figure 4b.
As described above, a difference occurs in the area of the wafer, and alignment is performed by feeding back this unbalance to the mask and wafer drive systems. Even when this alignment mark is used, the same effect as described above can be obtained.

FIG. 5 shows another embodiment of the invention. A combination of rectangular patterns whose widths are successively reduced is used as the alignment mark, and the same effect as described above can be obtained.

As explained above, according to the present invention, the present invention consists of an X-ray source section that is fixed during a series of exposure steps, a stage section on which a mask and wafer are mounted, and an alignment section, and is characterized by an asymmetrical metrological pattern of alignment marks. It is possible to obtain a practical and simple type of X-ray exposure apparatus that includes an alignment method using an X-ray flux having the following characteristics and that reliably guarantees copying in a submicron region. In the above description, the scope of the present invention also includes a case where a so-called half of a Fresnel zone plate or a similar pattern is used as the alignment mark. In addition, in the above explanation, only the method of detecting the irradiated X-rays passing through the mask and wafer has been described.
As shown in the figure, the same effect is obtained even when fluorescent X-rays transmitted through a mask and excited on a wafer are calibrated using a detector, and this is included within the scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional X-ray exposure apparatus, in which 11...fixed or rotating target, 12...electron beam, 13...soft X-ray,
14...Mask, 15...Substrate (wafer), 16...
These are a tube section, 17...sample chamber, 18...window section, 19...high vacuum evacuation section, 20...low vacuum evacuation section or He substitution section. FIG. 2 is a diagram of a conventional X-ray alignment system, in which 21...mask, 22... alignment mark on mask, 23... wafer,
24... Alignment mark on wafer, 25...
It is an X-ray detector. 3a and 3b are plan views showing one embodiment of the present invention, in which 31, 31', 33, 3
3'...Alignment mark on mask, 32,3
2', 34, 34'... Alignment marks on the wafer, 100, 100', 101, 101'... X-ray transparent areas. FIGS. 4a and 4b are plan views showing other embodiments of the present invention, in which 41, 41'... alignment marks on the mask, 42, 42'... alignment marks on the wafer, 200, 200 ′、
201, 201'...These are X-ray transparent regions. FIGS. 5a and 5b are plan views showing another embodiment of the present invention. FIG. 6 is a diagram of an alignment method using fluorescent X-rays.

Claims (1)

[Claims] 1. In an X-ray exposure apparatus that is equipped with an X-ray source section, a stage section on which masks and wafers are mounted, and an alignment section, these main sections are fixed during a series of exposure steps, and the alignment section is an alignment system using an X-ray flux. It has
A pair of alignment marks are formed on each of the mask and the wafer, and the total amount of transmitted X-rays is used for calibration as these alignment marks, and the pair of alignment marks on the mask or the wafer are moved in parallel. An X-ray exposure apparatus characterized in that it uses asymmetric metrical patterns that do not match even when there is a pattern.