JPH01214120A - Formation of pattern - Google Patents

Abstract

PURPOSE:To obtain an accurate pattern by conducting n-times of multiple irradiation of an electron beam with the dose of 1/n of a desired total dose to a pattern forming region, and sufficiently lengthening the radiation period in this case as compared with a noise period to be superposed on the electron beam current. CONSTITUTION:An electron beam is radiated in a desired radiation amount to a desired position on a resist which sensitively responds to the electron beam thereby to form a latent image of predetermined storage energy, i.e., pattern in the resist, and a resist pattern is formed by developing on a substrate. Thus, when the pattern is formed, the beam is scanned from a beam scan starting position Ps to its finishing position Pe by dividing the scanning into n times so that the total sum of the beam radiation amount after it is scanned n times coincides with the desired radiation amount. Thus, the variation in the radiation amount due to noise is reduced to 1n<0.5> times by the n-times of multiplex radiations. Thus, when the n is increased more, the storage energy distribution of the pattern region is uniformized, and a pattern of a high dimensional accuracy is obtained after a development.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a method for forming fine and highly accurate patterns by electron beam writing in the manufacture of semiconductor integrated circuits, optical integrated circuits, Josephson devices, etc. It is.

[Conventional technology]

The trend towards higher density and miniaturization of semiconductor integrated circuits is remarkable.
．． Advanced devices such as Si and GaAs devices in the 2 μm region or less are being developed. This trend is expected to continue in the future. Electron beam lithography, which can control ultrafine beams with high precision, is an effective method for forming nortans such as these ultrafine devices.

In the electron beam lithography method, a desired amount of electron beam is irradiated onto a desired position on a resist that is sensitive to electron beams to form and develop a certain accumulated energy distribution in the resist, that is, a latent image of a pattern. A resist pattern is formed on the substrate.

For the formation of ultra-fine patterns, it is important to control the irradiation amount with high precision, and for this purpose it is necessary that the beam current value be stable. However, in reality, the fourth
As shown in the figure, the beam current contains thermal noise, shot noise,
The beam current fluctuates because noise such as flicker noise is superimposed. The amount of noise varies depending on the type of electron beam source, and is about 2-3% for hot cathodes and about 5-30% for field emission cathodes. Also, the frequency of noise is approximately 1
It is known that the frequency is about 0Hz to 100kHz.

[Problem to be solved by the invention]

Conventional drawing methods have the following problems due to fluctuations in the dose due to noise.

FIG. 3 shows a conventional drawing method and a pattern shape after development. Normally, when applying a certain amount of irradiation to a desired pattern area, the beam irradiation time or scanning clock frequency is determined in advance based on the current value actually measured just before the start of writing and the following equation.

D=I-t/S=I/(p2 ・f) ・・・・・・
(1) Here, D: irradiation amount, I: beam amount, t: irradiation time, S: irradiation area, p: beam irradiation pitch, f: beam scanning clock frequency.

Under these drawing conditions, in the case of a point beam, Figure 3 (
As shown in a), the beam scanning start position P, (starting time 11
) to the beam scanning end position p and (end time ti), the drawing pattern W1 is drawn.

Figure 3(b) shows the fluctuation of the beam current I. The current value fluctuates from 11 to 2 due to noise between times t and t2, and the irradiation amount also fluctuates in response to this fluctuation. Therefore, the accumulated energy distribution within the irradiation area is not uniform.

Therefore, the pattern Wb after development has a shape as shown in FIG. 3(c), and there is a problem in that pattern dimensional accuracy and pattern quality deteriorate. In particular, this has been a big problem in the formation of ultra-fine patterns that require high dimensional accuracy.

This invention was made in order to solve the above-mentioned problems, and by irradiating the pattern forming area multiple times, fluctuations in the irradiation amount due to noise are reduced, making it possible to form extremely fine and highly accurate patterns. The object of the present invention is to provide a method for forming a pattern.

[Means to solve the problem]

In the pattern forming method according to the present invention, multiple irradiation is performed on the pattern forming area n times at a dose of 1/n of the desired dose, and at that time, the irradiation period is superimposed on the electron beam current. The period should be made sufficiently longer than the period of the noise generated.

[Effect]

In this invention, the influence of noise is suppressed by n times of multiple irradiation, and a highly accurate pattern can be formed.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

First, the principle of this invention will be explained.

Generally, the theory of synchronous addition in the time domain ("Digital Signal Processing" IEICE, ANALOG 5IGNAL PRO-
CESSING AND INSTRUMENTAT
ION CAMBRIDGE UNIV-ER5ITY
PRESS et al.) are known. If the input signal is sampled an appropriate number of times and accumulated with the time of a specific part of the input signal as the origin, the same signal will always be added, but noise has a different value each time, so the signal and noise ratio is improved in proportion to the square root of the number of additions. However, the sampling period should be long enough so that the sampled noise values have no correlation.

The above logic can be applied to the present invention by making the period of multiple irradiation sufficiently long compared to the period of noise.

An embodiment of the present invention will be described below based on the drawings.

In this invention, when it is desired to apply a certain amount of irradiation to a desired pattern forming area, multiple irradiation is performed n times, with each irradiation amount being D/n. Furthermore, the period T of irradiation is set to be sufficiently longer than the period of noise. SNR is the ratio of beam current to noise
shall be.

The drawing method in the case of a point beam is shown in FIG. FIG. 1(a) shows the drawing pattern W1 as in FIG. 3(a), p, , p are the beam scanning start position and beam scanning end position, and FIG. 1(b) shows the drawing pattern W1. Base? ffi
The relationship between I and time is shown.

As shown in FIG. 1(b), from each time t1 to t2, t3
to t4, ..., the beam scanning start position tp and the beam scanning end position P between t2n-1 and t2T1.

The beam scans up to. The total number of beam scans is n times. At each irradiation time, the beam current I changes from 11 to I2, from I3 to I4, I2, as shown in Fig. 1(b).
n-1 to I2. It varies up to n. The irradiation amount D1 for each time can be expressed as follows.

DI=D/n+d11 (i=1.2.-・", n
)D=(ΣDi)=DΣdi where D/n is the dose due to beam current I, dl
is the radiation dose due to noise.

Since dl takes a random value for each irradiation, n is (1
), then Σdi becomes yam. If n is finite, the following formula is obtained.

D=(ΣDi)=D+Σdi=D (1+1/ (FW-5NR)) Thus, n
Due to multiple irradiation, the variation in irradiation amount due to noise is 1/f
By increasing n by a factor of T, the distribution of stored energy in the pattern region becomes uniform. Therefore, the drawing pattern W after development. As shown in FIG. 1(C), a pattern can be formed with high dimensional accuracy. When this invention is applied to actual LSI pattern drawing, etc., there are some points that require attention. According to the principle of this invention, the period of multiple irradiation must be made sufficiently long compared to the period of noise, so if only one pattern is irradiated n times in succession, the waiting time for drawing increases, and the overall Throughput decreases. Fortunately, the actual LSI pattern is as shown in Figure 2(a).
The main field F has many sub-fields Fs as in
There are a huge number of patterns, such as patterns ■, ■, etc., and these are distributed within the chip. In this case, as shown in FIG. 2(b), by performing multiple writing, it is possible to satisfy the condition that the irradiation period T is sufficiently longer than the noise period, and to eliminate wasted writing time.

Multiple irradiation is performed for (1) every certain number of patterns, (2) every sub-field (sub-direction area) F8, (3) every main field (main change area) F, (4) every certain drawing time. There is a repeating method, and an appropriate method may be selected in consideration of the performance of the device and the pattern drawing conditions. Also,
In the above embodiment, multiple irradiation was performed n times with a dose of 1/n of the required dose, =D2=-:-----=Dn, but D1≠D2≠... ...≠Dn
But you can get the same effect. However, D=D, +D2+
...-+ D nNext, a specific example of this invention will be described.

0.2μm x 1500μm using point beam
I changed the line and space pattern of [i. The number of lines is 1
There are 0 pieces. The sample was a St substrate coated with a positive resist for electron beams to a thickness of 0.5 μm. The beam pitch is 0.02 μm and the beam current is 3 nA. The amount of noise relative to the signal is 17%, and the frequency component of the noise is 10Hz.
~1kHz. The amount of radiation required to form the line pattern is 400 uC/cm2. The number of multiple irradiations n is 2
0 and the irradiation amount per time was 20 μC/cm 2 .

Irradiation was repeated every time 10 line patterns were drawn. The period of irradiation is 200 m5. Table 1 shows the beam scanning clock frequency used and the dimensional accuracy of the formed pattern. It can be seen from this that the pattern dimensional accuracy was improved by multiple irradiation.

Table 1 Furthermore, the present invention is effective not only in the case of a point beam but also in the case of drawing using a variable shaped beam.

In conventional writing using a variable shaped beam, the pattern area is irradiated with the beam in a single stroke according to the writing conditions of an appropriate beam size and irradiation time t. Beam irradiation is performed for an irradiation time of t/n, and this is repeated n times to perform drawing.

(Effects of the Invention) As explained above, the present invention performs multiple irradiation on a pattern forming area n times at a dose of 1/n of the desired dose, and at that time, superimposes the irradiation period on the electron beam current. Since the period is sufficiently longer than the period of noise, it is possible to reduce fluctuations in the irradiation amount due to noise without increasing the beam irradiation time, thereby making it possible to form extremely fine patterns.

Further, the present invention has the advantage that it is effective against noise in a wide frequency range not only at low frequencies but also at high frequencies.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the drawing method of the present invention.
Figure 1(a) shows the drawing pattern shape, Figure 1(b)
is a diagram showing the relationship between beam current and time according to the present invention, FIG. 1(C) is a diagram showing the pattern shape after development, and FIG.
), (b) are LSI pattern shape diagrams for explaining the drawing method of the present invention for multiple patterns, and diagrams showing the relationship between beam current and time, and Figures 3 (a), (b), and (c). is for explaining the conventional drawing method, as shown in Figure 1(a).
, (b) and (c), respectively, and FIG. 4 are copies of the waveform of noise superimposed on the beam current. In the figure, W is the drawing pattern, W8° is the drawing pattern after development, P8 is the beam scanning start position, P is the beam scanning end position, t+ and t2 are the times, and It and I2 are the beam currents. Figure 1 1+, I2 Figure 2 1 hour (1) Figure 3 1 @ between (1) Figure 4

Claims (1)

[Claims] In a method of forming a pattern by irradiating a desired position on a substrate coated with a material sensitive to electron beams with an electron beam to give a desired dose, the pattern forming area is set at 1/n of the desired dose. A method for forming a pattern, characterized in that multiple irradiation is performed n times with an irradiation dose of 1, and at that time, the irradiation period is made sufficiently longer than the period of noise superimposed on the electron beam current.