JPS6231816B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam exposure method using a rectangular electron beam with a fixed or variable shape. The present invention relates to a method of connecting to form an exposure pattern.

In recent years, with the trend toward higher performance and higher integration of integrated circuit devices such as LSI and VLSI, electron beam exposure methods have been used in their manufacturing. Instead of filling in the exposure pattern point by point with an electron beam, a fixed or variable shaped square (e.g. rectangular, square, etc.) electron beam is projected onto the wafer to create desired image elements, and these image elements are connected. Many electron beam exposure methods are used to form exposure patterns.

In carrying out this method, image elements obtained by projecting various square electron beams are placed at desired positions by deflection by an electron beam deflection means, movement of a stage on which a wafer is placed, or a combination thereof. Moving and connecting is performed.

However, when forming exposure patterns such as integrated circuit elements using this method, it is necessary to avoid discontinuities (gaps due to insufficient connections, double exposure due to excessive connections, etc.) at the connection boundaries of connected image elements. It is. This is because this discontinuity directly affects the characteristics of the circuit.

Therefore, conventionally, various ideas have been devised for connecting the image elements. One of these methods is to utilize the Gaussian distribution of the electron beam to connect the boundaries at half-width of the Gaussian distribution.
(No. 24833), which connects image elements by reducing the amount of exposure at the adjacent ends of the image elements to be connected by gradually expanding or contracting the cross-sectional shape of the electron beam, or by gradually moving the electron beam and the wafer relative to each other. (Unexamined Japanese Patent Publication No. 54-25596) has been proposed.

However, in this method, because the half width of the Gaussian distribution of the beam itself is small (approximately 0.2 to 0.3 μm), high accuracy (approximately 0.1 μm or less) is required for beam projection positioning, and the beam position control system will be very expensive. The method described above attempts to improve this, but the beam control required for enlarging/reducing the cross-sectional shape of the beam or for relative movement of the beam and the wafer becomes complicated.

The present invention eliminates the drawbacks of the conventional methods described above, and aims to provide a method of connecting image elements to form an exposure pattern using an extremely simple method, and an apparatus for carrying out the method.

The purpose of this is to selectively expose out of focus only the connecting ends of adjacent image elements to be connected, and expose the parts of the image elements other than said ends in focus, thereby forming a given exposure pattern on the wafer. This is achieved by doing.

Furthermore, this purpose is to arrange the opening ends of the beam shaping mask, which is arranged along the beam projection path from the electron beam source to the exposure surface, at a position where the exposure surface is brought out of focus and a position where the exposure surface is brought into focus. This is accomplished using an electron beam exposure device.

Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings. FIG. 1 shows an example of a projection optical system in which the present invention is applied to an electron beam exposure apparatus using a fixedly shaped rectangular electron beam. An electron beam from an electron beam source 1 is irradiated by a focusing lens 2 and a deflection means 3 onto a beam shaping mask 5 having an aperture 4 with steps. The light beam is focused, deflected, and projected onto the wafer 8, and the rectangular image elements formed on the wafer are connected to form an exposure pattern.

Now, as shown in the figure, the stepped opening 4 of the mask 5
When the upper end 5a is just placed at the focal point 29 on the wafer, the edge 9 of the beam cut by the upper open end is as shown in the beam profile of FIG. In contrast to the sharp edges on the wafer, the lower open end 5b has a step D.
The edge 10 of the beam cut by is blurred, and the beam half width becomes wider.

Therefore, as shown in FIG. 3, by using a beam shaping mask 5 having various combinations of stepped rectangular apertures 4 and selectively irradiating each aperture, a desired shape of the rectangular beam can be obtained. Beams can be shaped to blur the edges and sharpen the remaining edges. In other words, by using a beam shaped in this manner, it is extremely easy to selectively defocus the edges of the image elements to be connected on the wafer.

4 and 5 are perspective views showing embodiments of a beam shaping mask having a stepped aperture used in the present invention. However, FIG. 4 shows a partial cross section.
The mask shown in Fig. 4 is constructed by adding a step D to two slits 5' and 5'' each having a rectangular opening 4. Depending on how the upper and lower masks are shifted, beams can be formed at the edges of the openings in various combinations. can be shaped.
As shown in the figure, the aperture is such that the upper mask 5' is shifted to the right with respect to the lower mask 5''. Therefore, when a beam enters from above, the beam is shaped by edges a and b'. The figure shows the edges a and c of the rectangular opening 4.
This is a single mask 5 with a step D at b and d. The beam is shaped at all edges, but edges a, c
When placed at a focusing position with respect to the wafer, the beam cut by edges b and d will blur on the wafer.

Note that the step D at the edge of the opening can be expressed by the following equation.

Dδ ₂ /α However, α: Beam opening half angle δ ₂ : Beam blur amount Therefore, for example, δ ₂ = 1 to 2μ, α2
In the case of ×10 ^-3 , D may be set to 0.5 to 1 mm. Normally, the step D may be set within a range of several mm or less.

FIG. 6 is a plan view showing an example of the arrangement of the apertures 4 of the mask 5 having stepped apertures in the exposure apparatus (FIG. 1) using a fixed shaped beam. In the figure, the aperture is shown by a solid line and a broken line.The solid line shows that the beam cut there focuses on the wafer, and the broken line shows that the beam cut there focuses on the wafer. It shows that something is going to happen. By selecting and irradiating the apertures arranged in this way with a beam, it is possible to project a beam onto the wafer with arbitrary edges blurred, and as a result, the connecting ends of adjacent image elements on the wafer can be selectively focused. It can be exposed to light.

FIG. 7 shows an example in which the present invention is applied to an exposure apparatus using a variable-shaped rectangular electron beam using a projection optical system. The beam cross-sectional shape and size are variably shaped by two sets of masks 5 ₁ and 5 ₂ each having a stepped aperture 4, a focusing lens 11 and a deflection means 12 arranged between them, and the other configuration is as follows. It is similar to FIG. In the figure, the upper edges of the apertures of each mask are arranged at focusing positions 2f ₁ and 2f ₂ .

FIG. 8 shows masks 5 ₁ , 5 with stepped apertures in an exposure apparatus using a variable-shaped rectangular electron beam.
₂ shows an example of the arrangement of the openings. In the figure, the meanings of the solid line part and the broken line part (in each opening) are the same as in the case of FIG. 6, and the dashed-dotted line can be either one. The aperture 4 of the upper mask ₅₁ cuts the beam at the right and front edges, and the aperture 4 of the lower mask ₅₂ cuts the beam at the left and opposite edges. By appropriately selecting the openings of the upper and lower masks, it is possible to shape a variable-shaped beam with arbitrary blurred edges.

As described in detail above, the present invention uses a beam shaping mask having a stepped aperture to very easily selectively expose out-of-focus the connecting ends of adjacent image elements to be connected.

[Brief explanation of the drawing]

FIG. 1 shows an example of a projection optical system in which the present invention is applied to a fixed-shaped electron beam exposure apparatus. FIG. 2 shows the beam profile obtained using the apparatus of FIG. FIG. 3 is a cross-sectional view and beam profile showing an example of a beam shaping mask having a stepped aperture used in the present invention. 4 and 5 are perspective views showing an embodiment of a beam shaping mask having a stepped aperture used in the present invention, and FIG. 6 is a plan view showing an example of the arrangement of the mask apertures used in the apparatus shown in FIG. FIG. 7 shows an example of a projection optical system in which the present invention is applied to a variable shaping electron beam exposure apparatus. FIG. 8 is a perspective view showing an example of the arrangement of openings in a mask used in the apparatus shown in FIG. Symbols in the figure: 1... Electron beam source, 4... Stepped aperture, 5, 5 ₁ , 5 ₂ , 5', 5''... Beam shaping mask, 5a, 5b... Edge of aperture (edge), 8... Wafer (Exposure surface), 9, 10... Edge of beam, D... Step, a, b, c, d... End (edge) of aperture.

Claims (1)

[Claims] 1 In an electron beam exposure method that connects a plurality of image elements to form a pattern, only the connecting ends of adjacent image elements to be connected are selectively exposed to defocus light, and the portion of the image element other than the connecting ends is in focus. An electron beam exposure method comprising aligning exposure to form a predetermined pattern on a substrate.