JPH0713937B2 - Electronic beam exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In the electron beam exposure method of the present invention, the correction of the aberration of the electron optical system is complemented by the correction of the input signal of the electrostatic sub-deflector to reduce the throughput. It realizes the improvement of the resolution.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam exposure method, and more particularly to improvement of an aberration correction method for an electron optical system.

The electron beam exposure method not only has a high resolution, but also has an advantage that the function as a pattern generator and the manufacturing time are shortened, and greatly contributes to the pattern formation of a semiconductor integrated circuit device (IC) or the like.

To further miniaturize the electron beam exposure pattern, further improvement in resolution is required, but in order to make this compatible with throughput, improvement in aberration correction method of the electron beam optical system is required.

[Conventional technology]

The electron optical system of the electron beam exposure apparatus includes, for example, as shown in FIG. 2, an electron gun 11, a blanking electrode 12, an illumination lens 13,
Apertures 14 and 17, molded deflector 15, molded lens 16,
It comprises a reduction lens 18, a projection lens 19, deflectors 20, 21, an aberration correction coil 22 and the like.

The electron lens used here is usually of a magnetic field type. For example, the projection lens 19 is integrated with the deflector 20 and the aberration correction coil 22, and the deflector 21 is provided in the vicinity thereof. The aberration correction coil 22 mainly corrects astigmatism. As shown in the schematic diagram of FIG. 3, the four poles that form the magnetic field as shown by the arrows are arranged at a 45 degree offset, and the magnetic field is superimposed. Has become.

In such an electron beam exposure apparatus, for example, in the main field having a side of about 10 mm, the main deflector 20 deflects the electron beam to the center of a subfield having a side of about 10 mm.
With this center as a reference, the sub deflector 21 deflects to each exposure position in the subfield.

Since the aberration of the electron optical system changes depending on the distance from the optical axis, the correction amount of the aberration has to be originally selected according to the exposure position, but conventionally the current value passing through the aberration correction coil 22 is selected for each subfield. , The correction amount of aberration is 1
It is a constant value within one subfield.

[Problems to be solved by the invention]

As described above, according to the conventional method of selecting the aberration correction amount to be a constant value for each subfield, in the subfield or the like which is located in the peripheral portion of the main field and has a large distance from the optical axis, the aberration is rapidly increased. Even if the aberration is corrected with reference to, the electron beam is blurred due to the remaining aberration as the distance from the center of the subfield is increased, and the resolution is reduced. Therefore, in order to miniaturize IC patterns and increase the scale of integration, it is necessary to improve the resolution especially in the peripheral portion of the main field.

As a means for this, for example, the aberration correction value is set to the sub-deflector 21.
A method of selecting for each deflection of the electron beam due to However, the aberration correction coil 22 is a magnetic field type, and the duration of the transient phenomenon is long when the current value is changed as compared with the sub-deflector 21 which is usually an electrostatic type, and the output settling time is, for example, several tens of μsec or more. This results in an increase in the throughput of the exposure process and a decrease in the throughput of the exposure process.

There is a strong demand for an electron beam exposure method that can cope with such a situation and improve the above-mentioned aberration correction without lowering the throughput.

[Means for solving problems]

The aforementioned problem is that the aberration correction of the electron optical system is performed with a uniform correction amount for each subfield selected by the main deflector, and the input signal of the electrostatic deflector for selecting the exposure position within the subfield. Is solved by the electron beam exposure method according to the present invention which complements astigmatism correction.

[Action]

According to the present invention, for example, by the aberration correction coil, the aberration correction of the electron optical system having a uniform correction amount for each subfield is performed in the same manner as in the conventional case, and the shortage or excess of the correction amount remaining by this aberration correction is performed. Usually, it is supplemented by correcting the input signal of the electrostatic sub-deflector for each exposure position.

That is, when one pixel in a certain pattern in a certain subfield is exposed, the electron beam is deflected to the position (ξ, η) of the pixel by the deflection (X, Y) by the main deflector and the sub deflector. The sum of the deflection (x, y) and ξ = X + x; η = Y + y (1)

In general, the astigmatism amount S (ξ, η) is approximately S (ξ, η) = αξ ³ + βη ³ + γξ ³ η
³ ≈αξ ³ + βη ³ (2), and from the above formula (1), S (ξ, η) = αX ³ + βY ³ + 3αX ² x + 3βY ² y + 3αXx ² + 3βYy ² + αx ³ + βy ³ (3) .

The conventional constant aberration correction for each subfield is to correct only αX ³ + βY ^{3 in} the first row on the right side of the equation (3).
Aberrations in the second row and below remain. In the present invention, this formula (3)
The correction of the first row on the right side is realized by a conventional method, and the correction of the second and subsequent rows is realized by correcting the input signal of the electrostatic sub-deflector.

The addition of the aberration correction term according to the present invention involves a slight change in the gain correction coefficient and the like in the conventional correction of the input signal of the sub-deflector, but the aberration is well corrected and the cross section of the electron beam is sharp. The position can be adjusted to a desired position on the surface to be exposed, and the resolution can be improved without increasing the output settling time of the electrostatic sub-deflector of, for example, about 100 nsec.

〔Example〕

 The present invention will be specifically described below with reference to examples.

When the value of (X, Y) in which the residual aberration in the second row on the right side of the above equation (3) is particularly large is large, 3αX ² x + in the second row
3βY ² y becomes dominant.

As shown schematically in FIG. 1, the electrostatic deflector has eight electrodes D ₁
When an apparatus is provided with a to D _8, the first direction for example X-axis direction and, the second row of components in the second direction forming an angle of 45 degrees with respect to this (s _1, S ₂₎ Is s ₁ = a ₁ X ² x + b ₁ Y ² y s ₂ = a ₂ X ² x + b ₂ Y ² y (4) or using a _{11 to} a ₂₂ determined for each subfeed, S ₁ = a ₁₁ It is expressed as x + a ₁₂ y S ₂ = a ₂₁ x + a ₂₂ y (5).

In the aberration correction according to the present invention, the calculation time can be shortened by using the equation (5). To implement this method, a constant a ₂₂
It is necessary to obtain the constant value that makes the peak of the backscattered electron detector the steepest by using a sample with many electron beam focus detection marks arranged in the main field. It is a practical method to obtain it, and if necessary, interpolate the intermediate position of the detection mark and store this.

The deflection signal voltage to be input to the sub-deflector is adjusted to V for each of the X-axis positive direction electrode D ₁ and the Y-axis positive direction electrode D ₃ , including conventional corrections such as gain, rotation, trapezoidal distortion, and offset. _X, if indicated as V _Y, the voltage V ₁ ~V ₈ for each electrode D ₁ to D _8, And correct it.

The correction calculation by the equations (5) and (6) has the same format as the gain and rotation correction calculation that has been conventionally performed, and these calculations can be collectively performed.

By applying the above-described correction to the wafer direct exposure of a large-scale semiconductor integrated circuit device, a pattern having practically no difference from the central portion in the peripheral subfield is obtained.

In the case of the above equation (4), constants a ₁ , a ₂ , b ₁ , b ₂
Is similarly obtained using, for example, focus detection marks provided at the four corners of the main field, and calculation is performed according to equations (4) and (6).

〔The invention's effect〕

As described above, according to the present invention, good resolution can be achieved even in the periphery of the main field even for a fine exposure pattern, and the density of semiconductor integrated circuit devices can be increased and the scale can be increased without lowering the throughput. A remarkable effect is obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrostatic deflector, FIG. 2 is a schematic diagram of an electron optical system of an electron beam exposure apparatus, and FIG. 3 is a schematic diagram of an aberration correction coil. In the figure, D _{1 to} D ₈ are electrodes of the electrostatic deflector, 11 is an electron gun, 12 is a blanking electrode, 13 is an illumination lens,
Reference numerals 14 and 17 denote apertures, 15 a shaping deflector, 16 a shaping lens, 18 a reduction lens, 19 a projection lens, 20 a main deflector, 21 a sub-deflector, and 22 an aberration correction coil.

Claims (1)

[Claims] 1. An astigmatism correction of an electron optical system is performed with a uniform correction amount by an astigmatism correction coil for each subfield selected by a main deflector, and an exposure position is selected within the subfield. An electron beam exposure method, wherein the astigmatism correction is complemented by correction of an input signal of an electrostatic sub-deflector.