JPS5948538B2 - Electron beam exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam exposure method using a fly fender spot method, and particularly to an exposure method for creating minute pattern portions with high precision.

In electron beam exposure using the flyshida spot method, the exposed surface is divided into a large number of minute points, and the electron beam is controlled on and off according to the exposure/non-exposure data for each point. By projecting a beam onto the exposed surface and developing it, the exposed surface, that is, the photosensitive resist film, is patterned into a desired shape.

If the electron beam has a uniform electron density in its cross section, and if the resist film is uniformly exposed only in the beam-irradiated areas and non-exposed in the non-irradiated areas, then the beam now forms a square cross-section with side d. If n pieces of these are closely arranged in a line, that is, if the beam is deflected in one direction by a distance d and irradiated n times, a rectangular pattern of width d and length nd will be created on the resist film, that is, a positive type. If you use a negative type, you can make holes in a similar pattern to the resist film, and if you use a negative type, you can leave the resist film in a similar pattern.

Repeat the beam once, then twice in a row with an interval.
Furthermore, if the projection is performed three times in succession at intervals, it should be possible to create a square pattern with l side d, a rectangular pattern with length d and width 2d, and a rectangular pattern with length d and width 3d.
However, in general, the electron density in the cross section of the beam is not uniform but has a Gaussian distribution, and the cross section is not necessarily narrowed down to the intended size, so the resist film is exposed to the beam irradiation. Light is received not only at the planned point but also around it.

Furthermore, although a resist film is coated on a substrate such as a silicon dioxide layer, when it is irradiated with a beam, it is also exposed to electrons reflected from this substrate, and these electrons may vary depending on the material and physical condition of the substrate. Although it varies depending on the temperature, it is generally scattering, so it exposes a wide area to light. In other words, the exposure state of the resist film by one beam irradiation is determined by the sum of the Gaussian distribution 1 of electrons in the beam itself and the Gaussian distribution 2 of reflected electrons, and the amount of received light Q, Al,
A2 is a constant, and Wl and W2 are beam spreads in 1/e width.

An outline of this Q(X) is shown in FIG. Since the exposure state is as described above, when multiple beams are projected, they overlap each other, and the exposed area extends not only to the range of Dxnd in the above example, but also to its surroundings, and the peak value of the exposure amount is also the same as the number n of beams.
It will change depending on.

Figure 1 is a diagram explaining this. A shows the case where -1 beam is irradiated to the point P1, B shows the case where three beams are projected adjacent to the points P2, P3, and P4, and C shows the case where three beams are projected adjacent to the points P5 to Pl2. The case where 8 consecutive projections are performed is shown. In the case of A, the exposure dose distribution Qx shown in Fig. 1 is obtained, but in the cases of B and C, the distributions Q(X) are partially overlapped, and the peak values of the exposure doses are the same as those of A, B, C
becomes larger in the order of Of course, this increase in peak value does not continue indefinitely, and as the number of adjacent points P5, P6, etc. increases, one Gaussian distribution will not substantially affect other Gaussian distributions. It reaches saturation at that point. Also, the protruding parts on the periphery settle down to a certain value as the number of points increases. The exposure amount peak value QP6 in this saturated state is I
If T is the beam current value, T is the beam projection time at one point, and a is the point interval, it is expressed by the following formula. By the way, the resist film that has been exposed to light as described above is then developed, and this development is
It is appropriate to carry out development so that the portion that receives up to half of the exposure amount Qps expressed by equation (2) is developed.

That is, in FIG. 2, it is appropriate that the portion above level L be developed. Therefore, patterns with lengths and/or widths exceeding a certain level can be obtained as specified, but
In the case shown by B below this, the pattern is too narrow, and furthermore, in the case shown by A, the pattern cannot be drawn at all. The present invention improves this point, and even small patterns can be easily
``The aim is to make it possible to create as desired.

The present invention divides an exposure surface into a large number of minute points, controls an electron beam according to data that determines whether each point is to be exposed or not, and projects this controlled electron beam onto the exposure surface. In an electron beam exposure method for forming a desired exposure pattern on the exposure surface by Relational expression a is the exposure point interval, B and C are coefficients corresponding to the half-width of the electron beam, and from this function expression, the exposure data Px
The method is characterized in that the width of the exposure pattern actually obtained is made as desired, and this will be described in detail below with reference to examples.

Exposure data, that is, data Px that specifies one-point projection, three-point continuous projection, etc. as shown in A, B, etc. shown in Fig. 1, and the pattern obtained by actual development. Width (
When the relationship with length) Hx is plotted, a relationship as shown in FIG. 2 is obtained.

In this figure, the straight line C1 shows the ideal state when Hx is proportional to Px, and the curves C2, C3, and C4 each represent the beam's 1
/Eri] W1 is 0.36 μm, 0.48 μm, 0.6
The λ-Hx relationship at 4 μm is shown. As can be seen from these curves, the smaller the exposure data, that is, the designed pattern width, and the thicker the beam used, the thinner the actually obtained pattern width becomes. These curves C-C4 can be expressed by the following formula. Here, B and C are coefficients of 1 of the Gaussian distribution.
/e Determined by width, etc.

Further, a is the point interval as described above. To find the coefficients B and C of this equation (3), we can transform this equation (3) as follows.

FIG. 5 illustrates this equation (5), and the straight line C.
,c. , C7 has b = 0.8, b = 1.0, b = 1.
Corresponds to 3. The coefficient c is the slope of these straight lines and is equal in both cases and calculates to 0.6. This coefficient c is considered to be a value that depends on (W,/a), but it is 1/Ell]W of the Gaussian distribution of backscattered electrons. is almost constant and does not change in the normal usage range. The coefficient b is (
The values shown in FIG. 4 are taken as W,/a) changes. Determine the coefficients B and C as described above, and correct the number of exposure points to expose the desired pattern using equation (3) so that the pattern width Hx becomes the desired value. The pattern width Hx is obtained.

For example, in the example shown in Figure 1, when creating a square pattern of DXd, the pattern cannot be formed by projecting one beam, so three beams are projected adjacently as in case B. Create the planned DXd square pattern. Note that this is not limited to the above-mentioned linear pattern, but can also be applied to rectangular patterns and other arbitrary shaped patterns. As explained in detail above, according to the present invention, fine patterns can be created almost as planned, improving the precision and reliability of pattern creation by electron beam exposure, and expanding its range of applications. .

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the number of beam projections and the exposure amount.
Figure 2 is a graph showing the relationship between exposure data and actually obtained patterns, Figure 3 is a graph showing exposure dose distribution characteristics,
FIG. 4 is a graph of the coefficient b, and FIG. 5 is a graph illustrating the relational expression. In the drawing, Px is exposure data, Hx is pattern width, P,,P
.

Claims (1)

[Claims] 1. An electron beam is controlled according to data that determines whether to expose or not to expose each point by dividing the exposure surface into a large number of minute points, and directing this controlled electron beam onto the exposure surface. In an electron beam exposure method in which a desired exposure pattern is formed on the exposure surface by projection, exposure data Px indicating the number of consecutive exposure points and an exposure pattern width obtained by projecting an electron beam according to the data are provided. Relational expression Px with Hx
=(Hx)/(a) [1+bexp(-cHx)] where a is the exposure point interval, b and c are coefficients corresponding to the half-width of the electron beam, and the exposure data Px is obtained from the functional formula. An electron beam exposure method characterized by exposing to light and adjusting the width of the exposure pattern actually obtained as desired.