JPS63155724A - Charged particle beam lithography method - Google Patents

Abstract

PURPOSE:To accurately form a resist pattern with good reproducibility by using total of first irradiation amount which is constant in a pattern region and zero in a nonpattern region and specific second irradiation amount as an irradiation amount. CONSTITUTION:A pattern region is divided to rectangular small regions (shots) subjected to a lithography by one forming beam, 1.0 is set as first irradiation amount to each shot, and registered with lithography data. Then, data of nonpattern region in which the white and the black of the pattern are inverted is obtained, divided to shots, 0.0 is set to each shot as first irradiation amount, and additionally registered to the lithography data. Second irradiation amount determined by the pattern shape calculated by using the shot of the nonpattern region existed within 20mum of radius from the center of one shot and a coefficient representing the scatter of electrons is added to the first irradiation amount of the shot(j)as an irradiation amount set value. An accurate resist pattern is obtained by using the data with good reproducibility.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a method for drawing fine patterns of semiconductor integrated circuits, etc. using a charged particle beam, and in particular to a method for drawing fine patterns of semiconductor integrated circuits, etc. using a charged particle beam. The present invention relates to a method for correcting a decrease in dimensional accuracy of a pattern caused by scattering.

(Prior Art) In recent years, various charged particle beam drawing devices have been used to draw fine patterns on samples such as semiconductor wafers. When forming a pattern using an electron beam exposure device, electrons are scattered within the sample, and the scattered electrons also expose parts of the resist coated on the sample other than the incident point. Due to this influence, the resist pattern after development differs from the desired shape and dimensions. This is a phenomenon called the proximity effect.

The Ghost method has been proposed as one method for correcting this proximity effect.

This is done by first drawing a desired pattern on the resist at a constant irradiation dose without taking the focus of the electron beam off the sample surface, then by using an electron beam with the focus off the sample surface. , a method in which a pattern in which the black and white of the above pattern is reversed is drawn for a second time using a predetermined irradiation amount. The effectiveness of this correction method has been confirmed by the formation of a 0.25gn resist pattern.
There were the following problems.

During the second drawing, it is necessary to align the drawing using an electron beam whose focus is removed from the sample surface and whose dimensions are widened. However, the beam size at this time is, for example, 12 μm when the accelerating voltage is 50 kV, so there is a large error in detecting the reflected signal from the alignment mark with a pattern width of about 1 m. Controllability and reproducibility of resist pattern dimensions will be significantly degraded.

(Problems to be Solved by the Invention) As seen above, the Ghost method has a major problem at a practical level: low controllability and reproducibility of resist dimensions due to widening the electron beam dimensions. there were.

The purpose of the present invention is to solve the problems of the prior art,
An object of the present invention is to provide a method for forming a resist pattern with high precision and high reproducibility.

[Structure of the invention]

(Means for Solving the Problems) When drawing a pattern using a charged particle beam, the present invention first provides a pattern area that is irradiated with charged particles when performing normal drawing, and a pattern area where charged particles are irradiated when performing normal drawing. Divide each non-pattern area into small areas where the line is not irradiated,
Next, for all of the small areas, the first irradiation amount is a constant value inside the pattern area and zero inside the non-pattern area, and the second irradiation amount is determined by a coefficient representing the shape of the pattern and the scattering state of electrons. A pattern in which charged particles are irradiated to all small areas inside the pattern area and non-pattern area according to the irradiation amount set for each small area. This is the formation method.

(Operation) FIG. 2 is a schematic diagram showing that the proximity effect is corrected by the conventional method. (a) and (b) are the irradiation dose distributions during the first and second irradiation using the conventional method, respectively. Moreover, (d) and (e) are the photosensitivity of the resist produced by electron beam irradiation of these distributions.

(c) and (f) are the first. This is the sum of the second irradiation amount and the sum of the exposure amount. As shown in the figure, when only the first irradiation is used, the amount of exposure is insufficient for small patterns because the backscattering effect from the electron base is small, but the second irradiation makes up for this shortfall. and by this, (f
), and the proximity effect is corrected.

In the method of the present invention, prior to drawing a pattern, the value obtained by adding the irradiation amount for the first drawing using this conventional method and that for the second drawing is set as the irradiation amount at each irradiation position. The pattern is drawn according to the set value without shifting the focus of the electron beam from the sample surface.

The dose set by the method of the present invention is the same as the effective dose when the conventional method is executed, and it is possible to obtain the same proximity effect correction accuracy as that obtained by the conventional method. Furthermore, since there is no need for the second drawing of the conventional method in which the focus of the electron beam is removed from the sample surface, the controllability and reproducibility deteriorated due to registration when drawing non-pattern areas, which existed in the conventional method. be excluded.

(Embodiment) FIG. 1 is a schematic configuration diagram showing an electron beam lithography apparatus to which an embodiment method of the present invention is applied. II in the figure is an electron gun, 1
2. ~, 16 are various lens systems, 17. ~.

19 is various deflection systems, 2o is a blanking plate, 21.22
2 is a beam shaping aperture mask, 23 is a backscattered electron detector, and 24 is a target. The electron beam emitted from the electron gun 11 is turned on and off by a blanking deflector 17. By adjusting the irradiation time at this time, this device makes it possible to change the irradiation amount depending on the irradiation position. The beam passing through the blanking plate 20 is shaped into a rectangular beam by the beam shaping deflector 18 and beam shaping aperture masks 21, 22, and the dimensions of the rectangle are varied. This shaped beam is then directed to a target 24 by a scanning deflector 19.
The target 2 is deflected and scanned by this beam scanning.
4 is drawn in a desired pattern. The acceleration voltage of the electron beam in this device is 50 kV, and the maximum size of the variable shaped beam that can be generated is 2 μm in height9.
It is a rectangle with a width of 2 μm.

The procedure for setting the irradiation amount is described below. FIG. 4 is a flowchart of the setting procedure. First, the pattern area is divided into rectangular small areas (hereinafter referred to as shots) that can be drawn with one shaped beam, the first dose is set to 1.0 for each shot, and the drawing data D1 is set to 1.0. register. Next, obtain the data of the non-pattern area by inverting the black and white of the pattern, divide it into shots, and add the first -
0.0 is set as the irradiation amount and additionally registered in the drawing data D1. The shaded areas in (a) and (b) in FIG. 3 indicate examples of pattern areas and non-pattern areas;
C) and (d) are examples of these shot divisions.

After such shot division, shots in a non-pattern area existing within a radius of 20 square meters from the center of one shot j are extracted.

In the following, this drawn shot will be abbreviated as a reference shot.

Examples of extraction of reference shots are shown in FIGS. 3(e) and 3(f), respectively, when shot j belongs to a pattern area and when shot j belongs to a non-pattern area.

Using the reference shot extracted in this way, however, ω=
σb/(1+η)1ha.

This means calculating the second dose Dadd determined by and adding this value to the first dose of shot j for all reference shots, rJ
and rk represent the coordinate values of shot j and the reference shot, and Sk represents the area of the reference shot. Also σb
is the spread of backscattering of the electron beam that occurs when the electron beam is incident on a resist on a silicon substrate at a single point, and η is the total photosensitivity of the resist due to forward scattering of electrons and the total photosensitivity due to backscattering. It is the ratio to the amount. The electron acceleration voltage of the electron beam drawing apparatus used in this example was 50 kV.

6tun and 1.0 were used for σb and η, respectively.

Here, the first equation above is an approximation of the amount of additional irradiation to position rj during the second drawing using the ghost method, and the error in this approximation is at most ±[1-exp(-(shot size) 2/(2ω)2)], and in the case of the above-mentioned drawing apparatus, it means an area integral over the entire area as small as about ±4%.

Using the drawing data D1 created in this manner, resist pattern formation experiments were repeated. As a result, a resist pattern with high dimensional accuracy and vertical shape was obtained with good reproducibility.

Furthermore, the minimum value m and maximum value M of the irradiance in the above-mentioned drawing data Dl are determined, and the value obtained by subtracting a constant value (m + -uniformity) from the irradiation amount of all shots is used as the new irradiation amount. Drawing data D2 was created as the setting value -m. However, in this case, the irradiation amount is from (-1 or -) to <M
Shots within the range up to m> were deleted from the drawing data. Using the drawing data created in this way,
When a pattern formation experiment was conducted, a resist pattern with high dimensional accuracy similar to the above example could be formed with good reproducibility.

Furthermore, since the irradiation amount could be reduced, the irradiation time was shortened and the throughput during drawing was improved compared to conventional methods.

The present invention is not limited to the above embodiments.

In the embodiment described above, the irradiation amount for each shot is set in the electron beam exposure data, but it may be performed in parallel with the writing inside the writing apparatus. That is, during the irradiation of a certain shot, the irradiation amount for another shot may be calculated by a dedicated circuit. Further, while a patterned area is being exposed, drawing data may be transferred in parallel processing and the irradiation amount for each shot may be calculated by a dedicated circuit.

〔Effect of the invention〕

According to the present invention, it is no longer necessary to perform alignment using an electron beam whose size is larger than the width of the alignment mark, which was the biggest cause of poor reproducibility in the conventional technology. The maximum proximity effect correction effect obtained can always be achieved with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electron beam lithography system to which an embodiment of the present invention is applied, FIG. 2 is a schematic diagram showing the principle of correction of the proximity effect, and FIG. 3 is a schematic diagram for describing an example of reference shot extraction. FIG. 4 is a flowchart showing the procedure for setting the irradiation amount. 11...electron gun, 12. ~, 16...
Lens system, 17, ~, 19... Deflection system, 21, 22... Aperture mask for beam shaping, 23
... Backscattered electron detector, 24... Target 31,
32... Aperture for beam shaping. Agent Patent Attorney Nori Ken Yudo Chika Kikuo Takehana (C) 2nd (f) Figures (a-) (C) (e) 3rd Cb) <d> (, f) Figures

Claims (3)

[Claims] (1) When drawing a pattern with a charged particle beam, the pattern area that is irradiated with the charged particle beam when performing normal drawing and the non-pattern area that is not irradiated with the charged particle beam when performing normal drawing are each small. The first radiation dose is approximately constant within the pattern area and approximately zero within the non-pattern area, and the second radiation dose is determined by a coefficient representing the shape of the pattern and scattering of electrons for all of the small areas. The sum of the irradiation amount and the irradiation amount of the small area is set as the irradiation amount of the small area, and then the charged particle beam is irradiated to all the small areas inside the pattern area and non-pattern area according to the irradiation amount set for each small area. A charged particle beam drawing method characterized by drawing a pattern. (2) In the charged particle beam lithography method according to claim 1 above, after setting the irradiation amount for each small area, a certain value is subtracted from the irradiation amount for all the small areas, and the value obtained thereby. A charged particle beam lithography method characterized in that: is set as a new irradiation dose setting value for each small area. (3) In the charged particle beam lithography method as set forth in claim 1 or 2 above, a charged particle beam lithography method is characterized in that the charged particle is not irradiated to a small area where the irradiation amount setting value is smaller than a predetermined value. Line drawing method.