JPS62287556A - Axis-aligning method for charged beam - Google Patents

Abstract

PURPOSE:To perform beam axis alignment with a few times of scanning, by detecting such a part as different in intensity or quantity of a beam by means of the scanning, and estimating an exciting quantity when the beam aligns its axis to an aperture hole, from the exciting quantity of an axis-aligning coil at that time. CONSTITUTION:An exciting quantity of a Y coil of an axis-aligning coil 11 is fixed, and synchronizing with scanning of an X coil of the coil 11, a reflected electron signal out of a limited aperture mask 12 is detected by a detector 13. Here, an X coil exciting quantity is set to a middle point Xc of detection signals Xa and Xb to be secured when a beam is scanned in an X direction so as to traverse a V-shaped groove 15 on the mask 15, scanning the Y coil of the coil 11, and the Y coil is set to a mid point Yf likewise. In succession, again scanning the X coil, the X coil is set a mid point X1. With suchlike operation repeated several times, beam axis-alignment to a mask aperture 14 is performable.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a charged beam lithography apparatus, and particularly to a method for aligning the axis of a charged beam.

(Prior Art) In recent years, electron beam lithography devices have been used as devices for forming fine, high-quality patterns for VLSIs and the like. Among electron beam lithography apparatuses, those using a variable beam beam type are particularly capable of performing lithography with high precision and high throughput. For this reason, it is impossible to transfer with light.
It is suitable as an apparatus for directly drawing a VLSI pattern with a design rule of [μm] or less on a wafer.

By the way, in this type of apparatus, in order to draw a pattern with high precision, it is necessary to align the electron beam with various lenses and various deflectors.

Alignment is accomplished by placing a limited aperture mask, usually with a small circular aperture, in or near the lens or deflector so that the center of the aperture coincides with the axis of the lens or deflector, and using an alignment coil. The beam is scanned over the aperture mask, the intensity or amount of the beam reflected from the mask, the beam passing through the mask, or the beam flowing into the mask is detected, and the axis is adjusted so that the intensity or amount is maximized or minimized. This is done by adjusting the excitation of the matching coil. FIG. 5 is a diagram illustrating an example of such an alignment method, in which a beam 20 is scanned over an aperture mask 22 by an alignment coil 21, and the beam reflected on the mask 22 is sent to a detector 23.
The beam can be aligned by detecting the reflected beam and adjusting the excitation of the alignment coil 21 so that the intensity of the reflected beam is minimized.

When aligning the beam axis using the method described above, if the amount of beam axis deviation is small, even if the range scanned by the alignment coil 21 is narrow, the intensity ('M) of the reflected beam will be the minimum point. Alternatively, it is possible to easily find the point where the intensity (amount) of the transmitted beam is maximum, but if the amount of axis deviation is large, it will appear in the shape of an IJ square as shown in Figure 6 or as shown in Figure 7. Unless a wide area is scanned in a spiral manner, the maximum or minimum point cannot be found, and it takes time to align the beam axis. In particular, when a limiting aperture mask is placed near the crossover due to the configuration of the electron optical system, both the beam diameter and the aperture diameter become small, resulting in a relatively large amount of axis misalignment, and it takes a lot of time to align the beam axis. There was a problem that required

(Problems to be Solved by the Invention) The present invention has been made in consideration of the above circumstances, and its purpose is to provide a method for aligning the axis of a charged beam so that the axis of the charged beam can be easily aligned in a short time. An object of the present invention is to provide an aperture mask for use in the present invention and a method for aligning the axis of a charged beam.

[Structure of the invention]

Means for Solving Problem C) In the present invention, the aperture mask has a part on the circumference centered around the aperture hole whose intensity formula or amount of reflected beam or transmitted beam is different from other parts, and the beam The beam alignment can be performed in a small number of scans by detecting areas where the intensity or amount of the beam differs by scanning, and estimating the amount of excitation when the beam is aligned with the aperture hole from the amount of excitation of the alignment coil at that time. This made it possible.

(Function) According to the present invention, by scanning the limiting aperture several times, the beam can be aligned with the limiting aperture, and by using fine adjustment that scans a small area, high precision can be achieved in a short time. This has the effect that beam alignment can be achieved.

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

FIG. 1 is a schematic diagram illustrating a beam alignment method in an embodiment of the present invention, in which 11 is an alignment coil, 12 is a limiting aperture mask, and 13 is a detector. FIG. 2(a) is a plan view of the limiting aperture mask 12 shown in FIG.
1 is a cross-sectional view, and the aperture mask 12 has a V-shaped groove 15 on the circumference around the mask hole 14. FIG.

Next, the alignment method in this embodiment will be explained. First, fix the amount of excitation of the X coil of the alignment coil 11,
A reflected electron signal from the limiting aperture mask 12 is detected by a detector 13 in synchronization with the scanning of the X coil of the alignment coil 11. Here, when the beam is scanned in the X direction so as to cross the V-shaped groove 15 on the limiting aperture mask 12 as shown in FIG. 3(a), the detection signal obtained is as shown in FIG. 3(b). xA and x correspond to the X coordinate of the V-shaped groove 15, respectively.

Next, set the excitation amount of the X coil to the midpoint of xA, Set the midpoint coordinate y. Subsequently, the X coil is scanned again to detect the coordinates xH of the V-shaped groove 15, and the X coil is set at the midpoint coordinate X1. By repeating this operation several times, mask hole 1
It becomes possible to align the axis to 4. Furthermore, after this, a small area around the mask hole 14 is closely scanned, and the excitation of the alignment coil 11 is set at the point where the detection signal is the minimum, thereby aligning the axis with the aperture center with high precision. Can be done. As described above, according to the present invention, beam alignment can be performed with high accuracy in a short time and with a small number of scans.

FIG. 4 is a schematic diagram illustrating an axis alignment method according to another embodiment of the present invention, in which the same parts as in FIG. FIG. 5 is a plan view of the limited aperture mask 12 shown in FIG. 4, and the aperture mask 12 has a group of small circular holes 15 on the circumference centered on the mask hole ]3. In this embodiment, the detector 13 is the aperture mask 1
This embodiment differs from the first embodiment shown in FIGS. 1 and 2 in that the transmitted electron signal from 2 is detected. The alignment method is the same as in the first embodiment except that a transmission electron signal is used, so detailed explanation will be omitted.

The limited aperture mask used in the present invention is not limited to the above-mentioned embodiments; for example, an aperture mask having circumferential protrusions is used instead of a V-shaped groove, and materials and structures that change the reflection or transmission of the beam are used. By doing so, similar effects can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, the effect of easily and highly accurate beam alignment can be obtained in a short time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining one embodiment of the present invention, FIG. 2 is a diagram showing an aperture structure, FIG. 3 is a diagram for detailed explanation of the present invention, FIG. FIG. 2 is an explanatory diagram showing a conventional scanning method. ]1... Alignment coil, 12... Limiting aperture mask, ]3... Detector. Agent Patent Attorney Noriyuki Chika Yudo Kikuo Takehana Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] In a charged beam alignment method in a charged beam lithography system that focuses and controls a charged beam emitted from a charged beam radiation source onto a sample surface, the reflected intensity of the beam is reduced around the alignment aperture where the charged beam is to be aligned. Alternatively, an aperture mask having portions with different reflection amounts, transmission intensities, or transmission amounts on a circumference centered on the alignment aperture, and an aperture mask disposed closer to the beam radiation source than the aperture mask, directing the beam onto the aperture. Using an alignment coil that scans at A method for aligning a charged beam by determining the axis of the charged beam and aligning the axis of the beam to the determined aperture position using the alignment coil.