JPS60231324A - Electron beam exposure apparatus - Google Patents

Abstract

PURPOSE:To obtain a high-performance apparatus which enables a clear beam image to be obtained over the entire deflection field, by providing a focusing coil and a plurality of astigmatism correction coils consisting of at least a twofold astigmatism correction coil and a threefold astigmatism correction coil, and supplying correction data to each of the coils. CONSTITUTION:Two kinds of astigmatism correction coils, that is, a twofold astigmatism correction coil 21 and a threefold astigmatism correction coil 22 are disposed together with a focusing coil 1. Correction data corresponding to each of the points in the entire deflection field is prepared for all of the coils and stored in the memory section of an arithmetic controller 8. The correction data is experimentally obtained for each of the points in the entire deflection field. For example, the deflection field is divided into a multiplicity of points, and a peak value of a curve obtained by differentiating a reflected beam detecting signal with respect to the value of current flowing through the focusing coil 1 is calculated for each of the points. In this way, data items for all of the points in the field are stored, and when the field is scanned, these data items are collated with each of the points in the field, and a beam image which has been corrected is projected.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an electron beam exposure apparatus, and more particularly to an exposure apparatus in which aberrations are highly corrected.

(bl Background of the Technology) In recent years, due to the limitations of ultraviolet exposure, electron beam exposure has been widely used, and it is well known that it is of great help in miniaturizing ECs (semiconductor integrated circuits).

On the other hand, there is no limit to the high integration of ICs, and as they become smaller,
Since circuits have advantages such as high-speed operation, efforts are being made to increase the integration and density of ICs. Therefore,
Recently, submicron patterns have been drawn, and it is extremely important for an electron beam exposure apparatus to scan the surface to be exposed with a beam spot as clear as possible.

(C) Prior Art and Problems Now, in a scanning electron beam exposure apparatus, the beam scans a flat wafer surface, so if it deviates from the center of the deflection field, it will no longer be focused on the wafer surface. That is, as the beam moves away from the center point of the deflection field, the focal length must be increased so that, for example, if the deflection field is square, the maximum focal length is at the four corners. Otherwise, proper focus cannot be obtained over the entire field.

A coil that functions in this manner is called a focus coil (dynamic focus coil), and has already been installed in exposure apparatuses.

Also, as the beam moves away from the center of the deflection field, the astigmatism of the beam changes, making it less sharply focused. That is, the beam is properly focused in one direction in a plane orthogonal to the deflection direction, but is out of focus in the other direction, resulting in a distorted elliptical beam spot. In order to correct this, an astigmatism correction coil (stigmator coil), like a focusing coil, has been installed in an electron beam exposure apparatus for some time.

Fig. 1 shows a schematic diagram of an electron beam exposure apparatus in which such a focusing coil 1 and astigmatism correction coil 2 are arranged, and the other symbols 3 are the electron gun, 4 is the blanking, and 5 is the aperture lens. , 6 is a deflection lens, 7 is a wafer (substrate to be exposed), and 8 is a calculation controller that controls the overall exposure apparatus.

Of these, the focusing coil 1 is a ring-shaped coil made of a bundle of conducting wires, and is installed around the deflection field area, while the astigmatism correction coil 2 has the center of the field as shown in Figure 2. It has a shape in which coils are arranged radially as a region. This coil has S poles and N poles adjacent to each other alternately, and the shape of the beam spot can be changed by adjusting the number of turns of the coil and the amount of current. Generally, a two-fold symmetrical astigmatism correction coil as shown in Fig. 2 is widely used, but instead of just one astigmatism correction coil, two coils of the same shape are provided.
One side is arranged planarly offset by 45 degrees from the other. The two-fold symmetric astigmatism correction coil is also called a quadrupole coil, but astigmatism correction coils with complex shapes such as three-fold, five-fold, and six-fold symmetry are also known.

However, one type of astigmatism 'R? It has been found from experience that it is difficult to completely correct aberrations using only the +Ii positive metal mirror. For example, a triangular beam spot tends to appear over the entire field,
It is very difficult to correct the beam spot to a highly perfect circular shape. On the other hand, if an astigmatism correction coil with a complicated shape such as 6-fold symmetry is used, the correction data becomes extremely complicated, and it is also extremely difficult to make the beam spot a highly perfect circle over the entire field. It becomes a karma.

Incidentally, the above-described problem of beam defocusing decreases as the electron gun 3 moves away from the wafer 7 surface, and correction becomes easier. However, this weakens the beam intensity and reduces the exposure amount.

The present invention relates to an electron beam exposure apparatus that can bring an electron gun closer to the surface to be exposed, in other words, increase the half-angle of convergence, widen the deflection angle, and obtain a strong beam, that is, improve the performance of an electron beam exposure apparatus. .

(d+ OBJECTS OF THE INVENTION The present invention provides a solution to the above-mentioned problems and provides a high-performance electron beam exposure apparatus that can obtain a clear beam image over the entire deflection field.

+01 Structure of the Invention The object is to provide a focusing coil and a plurality of astigmatism correction coils each consisting of at least a two-fold symmetrical astigmatism correction coil and a three-fold symmetrical astigmatism correction coil; aberration? This can be achieved by an electron beam exposure apparatus that provides correction data corresponding to each address of the deflection field to each of the di positive coils.

ffl　Embodiments of the invention Hereinafter, an embodiment will be described in detail with reference to one drawing.

FIG. 3 shows a schematic cross-sectional view of an electron beam exposure apparatus according to the present invention, and as shown in the figure, focal points 1 and 2 are
Two types of astigmatism correction coils, a rotationally symmetrical astigmatism correction coil 21 and a threefold symmetrical astigmatism correction coil 22, are arranged. The two-fold symmetrical astigmatism correction coil 21 is as shown in FIG. 2, and the shape of the three-fold symmetrical astigmatism correction coil 22 is shown in FIG. Although only one 3-fold symmetrical coil 22 is shown in the figure, like the 2-fold symmetrical astigmatism correction coil 2, there are two coils with the same shape, one of which is shifted by 30 degrees in plan with respect to the other. It is a coil consisting of.

In this case, a total of five coils will be provided including the focusing coil and the astigmatism correction coil, but correction data corresponding to each point in the field area will be created for all these coils, and the correction data will be adjusted accordingly. is stored in the storage section of the calculation processing device 8. The data can be obtained experimentally for each point in the entire field, but for example, as shown in Figure 5 (al), the deflection field area 10 is divided into many points, and for each point, the reflected beam for the current value of the focusing coil is Calculate the peak value P of the differential of the detection signal.The chart is shown in Figure 5 (hl), but this data can be obtained by, for example, scanning a certain area on the sample with a beam, and scanning the area at the edge of the area. It is obtained by differentiating the amount of change in the beam signal and plotting the value experimentally.In this way, data F is stored for all points in the field.Please note that the data F is stored for all points in the field. interpolates data from nearby points.

Similarly, in addition to the data of this focusing coil, for each point of the deflection field 10, data S in the X direction of the two-fold symmetric astigmatism correction coil 21 for each point of the field area.
, X-direction data Sy, X-direction data Hχ of the three-fold symmetric astigmatism correction coil 22, and y-direction data r1y.
and input them into the storage section of the calculation processing device 8.

Thus, when scanning the field, these data are checked at each point in the field area, and higher-order corrections are sequentially performed using the focusing coil, the 2-fold symmetrical astigmatism correction coil, and the 3-fold symmetrical astigmatism correction coil. project a beam image. Then, a perfectly circular beam spot is scanned over the entire deflection field. Also, it can be deflected to a wide angle to create a feel 1
: It is also possible to further widen the area.

According to the implementation results of the electron beam exposure apparatus constructed as described above, a perfect circular beam spot of 0.1 μmφ was obtained at the four corners of a 10 mm square field area, and a perfect circular beam spot of 0.1 μmφ was obtained at the four corners of a 151 m square field area. A beam spot of .2 μmφ was obtained, and other points near the center of the field also
A similar perfectly circular beam spot is obtained.

fgl Effects of the Invention As is clear from the above description, the present invention provides a high-performance electron beam exposure apparatus that constantly scans with an appropriate beam image, and greatly contributes to improving exposure precision.

In addition, is the above example a 2-fold symmetric astigmatism correction coil and a 3-fold symmetric astigmatism correction coil? Although the description has been made using the ili positive coil, it is natural that similar results can be obtained even if other symmetrical coils, for example, 5-fold symmetrical coils, are used instead of the 3-fold symmetrical coil.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a conventional electron beam exposure system, Figure 2 is a diagram illustrating one of the two-fold symmetric astigmatism correction coils, and Figure 3 is a diagram illustrating one of the two-fold symmetric astigmatism correction coils.
FIG. 4 is a schematic diagram of an electron beam exposure apparatus according to the present invention.
The figure shows one of the three-fold symmetrical astigmatism correction coil.
Figure 5+al is a diagram illustrating each point of the field, and Figure 5) is an example of a chart showing the peak value P of the beam. In the figure, 1 is a focusing coil, 2.21 is a 2-fold symmetrical astigmatism correction coil, 22 is a 3-fold symmetrical astigmatism correction coil, 3 is an electron gun, 4 is blanking, 5 is an aperture lens, and 6 is deflection. 7 is a wafer, 8 is a calculation controller, and 10 is a field. Fig. 1 Fig. 2 Fig. 13 Fig. 4, -B Fig. 5

Claims (1)

[Claims] A focusing coil and a plurality of astigmatism correction coils comprising at least two-fold symmetrical astigmatism-correcting coils and a three-fold symmetrical astigmatism-correcting coil are provided, each of the focusing coil and the astigmatism correction coil having a deflection field. An electron beam exposure apparatus characterized in that correction data corresponding to each address is given.