JPS624319A - Adjustment of image forming optical system - Google Patents

Abstract

PURPOSE:To facilitate adjusting parallelism of a forming beam by a method wherein fine heavy metal particles are scanned by the forming beam with a small width and the parallelism of the two facing sides of the forming beam is detected from a reflected electronic signal profile from the heavy metal particles. CONSTITUTION:The image of the aperture 13a of the first aperture mask 13 is projected and formed on the second aperture mask 15 by a projecting lens 14. Then, the shape of a beam passes through the aperture 15a of the mask 15 becomes a rectangular with dimensions (a)X(b) and its image is formed on the surface 18 of a specimen. If, at that time, the position of the beam image formation of the second aperture mask 15 is varied by a forming deflector 21 to reduce the dimension (b) gradually, the beam dimension at the specimen 18 becomes a resolution of the linear beam. Therefore, the beam density distribution is reduced in accordance with the access of the two sides to each other. If there is no parallelism between the two sides, the magnitudes of (b) at both ends of the beam are different from each other. Therefore, by detecting this beam density, the parallelism of the beam can be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention provides high-precision relative angular adjustment around the optical axis of an object surface or image surface of an imaging optical system used in a charged beam exposure device or the like. The present invention relates to a method for adjusting an imaging optical system.

[Technical background of the invention and its problems]

In recent years, various electron beam exposure apparatuses have been used to form desired patterns on samples such as semiconductor wafers and mask substrates. Furthermore, in order to increase the exposure throughput, research and development is also being conducted on a variable shaped beam type electron beam exposure apparatus in which the dimensions of the rectangular beam can be varied. A variable dimension beam type electron beam exposure apparatus irradiates an electron beam onto a first aperture mask having a rectangular aperture, and images the beam passing through the aperture of this mask onto a second aperture mask having a rectangular aperture. , the beam size is varied by changing the optical overlap of the apertures by deflecting the beam between each aperture mask.

By the way, the pattern formed on the sample has a thickness of 0.5 μm.
], and the beam shape is generally 10Eμm in order to shorten sample exposure processing time, limit uniformity of beam density, and reduce blur due to beam space charge effect.
] Possible to a degree. 0.5 [μm']
It is necessary to form a rectangular shaped beam of xl 0 [μm]. The dimensional accuracy of this shape can be determined by measuring the dimensions of the beam, but as shown in Figure 2, there is no highly accurate method for measuring the orientation of the aperture, which determines the parallelism of the two opposing sides, and in reality the images of the apertures of the aperture mask overlap. This was done by exposing the image to light and measuring its shape.

However, if the setting accuracy of the beam size 0.5 [μTrL] is 1/20, the aperture orientation accuracy is 0.5
[μ71A] X1/20X1/10-2, 5 [mr
ad], and it takes a lot of time to measure the exposed shape of the sample and operate the device, which is an important problem in practical use of the device. Furthermore, it is difficult to achieve this level of accuracy by incorporating an aperture mask, so the only way to find out the amount of rotation of the shaped beam was to assemble the aperture mask and then observe a sample that was experimentally exposed. . The only observation means available is an SEM (scanning electron microscope), which requires a large amount of measurement time and also requires skill in adjusting the rotation of the aperture mask.

Note that the above problem is not limited to electron beam exposure apparatuses, but also applies to ion beam exposure apparatuses. Furthermore, similar problems occur not only in charged beam exposure devices but also in exposure devices that use light, and not only exposure devices but also various devices that use shaped beams.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to easily and quickly adjust the aperture parallelism of two sets of aperture masks, and to improve the operating rate of exposure equipment. It is an object of the present invention to provide an imaging optical system adjustment method that can contribute to the present invention.

[Summary of the invention]

The gist of the present invention is to detect the beam intensity at each end of the two opposing sides of the shaped beam when they are brought close together,
Its purpose is to measure the parallelism of two sides.

That is, in the present invention, a beam emitted from a beam emission source is irradiated onto a first aperture mask, and the beam that has passed through the aperture of the aperture mask is irradiated by a first lens into a second aperture mask.
In an imaging optical system that images or directly irradiates a beam onto a second aperture mask and passes through an aperture of a second aperture mask to form an image on a sample surface, the beam is parallel to the sample surface. on the second aperture mask so that the two sides corresponding to each aperture edge of the first and second aperture masks, which should have a similar relationship, are imaged at a position separated by one degree or less from the resolution of the imaging system. Move the aperture image of the first 7 percha mask in
In this method, the first or second aperture mask is rotated so that the beam intensity at each imaging point of the adjacent end portions of the two sides is approximately the same.

〔Effect of the invention〕

According to the present invention, it is not necessary to once testly expose a sample, and there is no need to use a very expensive SEM, and the parallelism of the shaped beam p can be easily adjusted. In addition, even an unskilled person can easily adjust the rotation of the forming beam in about 10 minutes, which conventionally took a skilled person almost a day. Therefore, it is possible to significantly improve the operating rate of the charged beam exposure apparatus and the like.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing the structure of an electron beam exposure apparatus used in a method according to an embodiment of the present invention. An electron beam emitted from an electron gun (charged beam source) 11 is uniformly irradiated onto a first aperture mask 13 by a focusing lens 12 .

The beam that has passed through the aperture 13a of the aperture mask 13 is imaged onto the second aperture mask 15 by the projection lens 14. The beam that is shaped after passing through the aperture 15a of the aperture mask 15 is transmitted through the reduction lens 1
6 and an objective lens 17 onto a sample surface 18 .

A scanning deflector 19 is arranged between the lenses 16 and 17, and the beam position on the sample surface 18 is changed by this deflector 19. A blanking deflector 2o and a shaping deflector 21 are arranged between the aperture mask 13 and the lens 14. Then, the timing of beam irradiation is controlled by the blanking deflector 20. Furthermore, by changing the position of the beam imaged onto the aperture mask 15 by the shaping deflector 21, the dimensions of the shaped beam can be varied.

A predetermined deflection signal is supplied to the deflectors 19, 20, and 21 from a computer (CPU) 30 via an interface 32. That is, each deflection voltage is controlled by the CPU 30 according to the pattern data in the memory 31, and a predetermined deflection voltage is applied to each deflector 19, 20, 21, respectively.

On the other hand, above the sample surface 18, a backscattered electron detector 41 for detecting backscattered electrons is arranged. The detection signal of this detector 41 is supplied to a monitor 43 via an amplifier 42 and also to the CPU 30 via an A/D converter 44. The monitor 43 displays the profile of the reflected electron signal.

Further, each of the aperture masks 13, 15 has a structure in which it can be rotated by a drive mechanism 45.degree. 46 consisting of a rotary motor, a piezoelectric element, or the like. Then, by providing beam inclination information to the CPU 30 according to the display information on the monitor 43, or by the CPU 30, the beam inclination is determined based on the backscattered electron signal, and the aperture mask 13.15 is controlled to rotate according to this inclination. It has become something that will be done.

Next, a method for adjusting the parallelism of a shaped beam using the above device will be explained.

When the aperture 13a of the first aperture mask 13 is projected and imaged onto the second aperture mask 15 by the projection lens 14, the shape of the beam that has passed through the seven barges 15a of this mask 15 has dimensions <aXb as shown in FIG. It becomes a rectangle. This shaped beam is imaged onto the sample surface 18 by a reduction lens system (16° 17) with a magnification of 1/M.

The beam shape at the sample surface 18 is (a/M) x (b/M)
It becomes a rectangle. At this time, the shaping deflector 21 causes the second
changing the beam imaging position on the aperture mask 15,
As the dimensions are made smaller, the sample surface 1 becomes smaller as shown in Figure 3.
The beam size B at 8 is a value larger than b/M in a minute area, and roughly at b/M#0, B becomes the line beam resolution BO. This is because the blurring on the sample surface of the two opposing sides overlaps as the two sides get closer and eventually become the same.

Therefore, as the two sides are brought closer, the beam density distribution becomes
It decreases as shown in the figure.

Here, if the two sides are not parallel as shown in FIG. 5(a), the size of b will be different at both ends of the beam,
As shown in FIG. 2(b), there is a difference in beam density at the sample surface 18. Therefore, by detecting this beam density (beam intensity profile), the parallelism of the beam can be determined.

Therefore, the beam size is controlled by the shaping deflector 21 to such an extent that the two sides that should be in a predetermined size and in a parallel relationship are imaged at a position that is at or below the resolution of the imaging system,
As shown in FIG. 6, the shaped beam 51 is scanned by the scanning deflector 19 so that the shaped beam 51 passes over fine heavy metal particles 52 such as gold. Here, since the heavy metal particles 52 have a larger reflected electron coefficient than the sample surface 18, for example, the silicon (or carbon) surface, when the shaped beam 51 passes over the heavy metal particles 52, the reflected electron intensity is large. Become. The reflected electron profile (displayed on the monitor 43) obtained when scanning with the shaped beam 51 is as shown in FIG. That is, when the parallelism of the shaped beam 51 is deviated, FIGS. 7(a) and (C)
As shown in (b) of the same figure, the beam profile is tilted; when there is no tilt, the beam profile is uniform as shown in FIG.

Therefore, by rotating the aperture mask 13, 15 while observing this profile, the parallelism of the two pieces can be adjusted. In addition, aperture mask 1
3.15 can be rotated by the drive mechanism 45, 46 or a manual rotation introducing device from the outside.

Thus, according to the method of this embodiment, by scanning minute heavy metal particles with a shaped beam whose beam width is sufficiently small, the parallelism of two opposing sides of the shaped beam can be easily detected from the reflected electron signal profile. By rotating the aperture mask 13, 15 using this inclination, it is possible to eliminate deviations in the parallelism of the shaped beam. Therefore, unlike the conventional method, there is no need to test the sample to light, and there is no need to perform SEMII detection. It is possible to significantly improve the operating rate of equipment, and its usefulness in semiconductor manufacturing technology is enormous.

Note that the present invention is not limited to the method of the embodiment described above. For example, instead of rotating the aperture masks, the strength of the lenses between the two sets of aperture masks may be varied to rotate the shaped beam. It is also possible to automate the parallelism adjustment of the shaped beam by converting the backscattered electron signal intensity profile into a digital signal, calculating the slope of the profile using a computer, and then rotating the aperture mask using a motor, etc. It is possible.

Furthermore, as a means for detecting the deviation in parallelism of the shaped beam, secondary electrons from the sample surface may be detected instead of reflected electrons. Furthermore, the present invention is not limited to electron beam exposure apparatuses, but can also be applied to ion beam exposure apparatuses that use shaped beams. Furthermore, the invention is not limited to exposure apparatuses, but can also be applied to various apparatuses that use shaped beams. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 shows an electron beam exposure apparatus used in a method according to an embodiment of the present invention. A schematic configuration diagram, FIG. 2 is a schematic diagram showing the shape of the shaped beam due to the overlap of the first aperture image and the second aperture, and FIG. 3 is a characteristic diagram showing the change in beam dimension on the sample surface with respect to the set beam dimension. FIG. 4 is a characteristic diagram showing changes in beam density with respect to beam dimensions, FIG. 5 is a schematic diagram showing beam shape and beam density, and FIG. 6 is a schematic diagram showing the relationship between the scanning direction of the shaped beam and heavy metal particles. 7th
The figure is a schematic diagram showing the relationship between the beam shape and the backscattered electron signal profile. 11... Electron gun (charged beam source), 12... Focusing lens, 13... First aperture mask, 13a. 15a...Aperture, 14...Projection lens, 15
...Second aperture mask, 16...Reducing lens, 17...Objective lens, 18...Sample surface, 19...
・Scanning deflector, 20...Blanking deflector, 20・
... Molding deflector, 30... CPU, 31... Memory, 32... Interface, 41°... Backscattered electron detector, 43... Monitor, 45.46... Drive mechanism , 51... Shaped beam, 52... Heavy metal particles. Applicant's agent Patent attorney Takehiko Suzue 2y1

Claims (3)

[Claims] (1) A first aperture mask is irradiated with a beam emitted from a beam emission source, and the beam that has passed through the aperture of the aperture mask is imaged or directly irradiated onto a second aperture mask by a first lens; In an imaging optical system that images a beam shaped by passing through an aperture of a second aperture mask onto a sample surface, first and second apertures are arranged in a parallel relationship in the beam on the sample surface. moving the aperture image of the first aperture mask on the second aperture mask so that two sides corresponding to each aperture edge of the mask are imaged at positions separated by or less than the resolution of the imaging system; . A method for adjusting an imaging optical system, comprising rotating the first or second aperture mask so that the beam intensities at each imaging point on adjacent ends of the two sides are approximately the same. (2) The method for adjusting an imaging optical system according to claim 1, wherein the beam emission source is a charged beam emission source that emits an electron beam or an ion beam. (3) The imaging optical system adjustment method according to claim 1, wherein each aperture shape of the first and second aperture masks is rectangular.