JP2000306827A - Charged particle beam drawing apparatus and pattern formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To draw a micropattern with less proximity effect by providing an auxiliary exposure for irradiating a drawing region on a sample with an exposure amount for an auxiliary exposure figure and a main exposure for irradiating a drawing pattern region in the drawing region on the sample. SOLUTION: In the process for carrying out an auxiliary exposure over the whole surface of a drawing region 502, the drawing region 502 is divided into a plurality of small regions 503, 504 having equal area, and the value of the area to be irradiated by a charged particle beam is calculated for each small region 503, 504, and the calculated area value is modified by subjecting it to weighted addition of the area value of the peripheral small region thereof for each small region 503, 504. Then, a plurality of auxiliary exposure figures are formed for the whole surface of this drawing region 502, and an exposure amount for auxiliary exposure figure thus formed is determined with reference to the value of the modified area. Then, the drawing region 502 on the sample is irradiated by the exposure amount of the auxiliary exposure figure, and a drawing pattern region in the drawing region on the sample is exposed to main exposure irradiation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam drawing apparatus and a pattern forming method for drawing a fine pattern with a charged particle beam, and more particularly to a method for manufacturing a semiconductor integrated circuit having a very high degree of integration. A charged particle beam drawing apparatus and a pattern forming method are provided.

[0002]

2. Description of the Related Art With the development of the electronics industry, the miniaturization of circuit patterns of semiconductor integrated circuits is rapid. For forming such fine patterns, a drawing method using a charged particle beam with higher resolution has been used. Drawing by a charged particle beam has a disadvantage that the speed is slower than a method of transferring a circuit pattern drawn on a mask using light. However, using a charged particle beam whose cross section has a specific shape so that the charged particle beam passes through an aperture of a specific shape, collectively draws a fine pattern area of about 5 μm or 10 μm square at a time. The drawing method has been put to practical use, and the drawback of low speed has been gradually improved.

On the other hand, in a method of forming a circuit pattern using a charged particle beam, as the pattern becomes finer, a fine pattern and a fine width sandwiched between fine patterns and a fine width of a gap or a portion where sudden changes in dimensions occur. And a phenomenon that gaps and gaps are not formed to desired dimensions appears, which is a problem in forming a fine pattern. This phenomenon is an important problem to be solved in a fine pattern forming method using a charged particle beam, and is called a proximity effect. The cause of this phenomenon is that the irradiated charged particle beam passes through a photosensitive agent (hereinafter referred to as resist) and enters the semiconductor substrate, and a part of the backscattered charged particles in the substrate returns to the resist surface again. Exposure. Such charged particles are called backscattered particles. The backscattering particles have the same effect as when a drawing pattern blurred over a wide area is lightly exposed. Therefore, the exposure of the region having a high pattern writing density is excessively exposed due to the addition of the exposure by the backscattering particles, and appears as a phenomenon in which the line width and the width of the gap change as described above.

Conventionally, in order to reduce the influence of the proximity effect, as described in JP-A-3-225816 by the present inventors, the entire drawing area is divided into a plurality of small areas in advance and each An exposure area density method has been proposed in which the exposure area density is calculated and the exposure time is shortened in a small area having a large exposure area density, and the exposure time is lengthened in a small area having a small exposure area density.

As another method, G. Owen,
A paper by P. Risman, "Proximity Effect Collection for Electron Beam.
Lithography by Equalization of Background Doses, "Journal of Applied Physics, Vol. 54, No. 6, 3573-3.
581 pages (June 1983) (G. Owen and P. Rissm
an, "proximity effectcorrection for electron beam l
ithography by equalization of backgrounddose ", J.Ap
As shown in pl.Phys., Vol. 54, No. 6, pp. 3573-3581 (June 1983)), the focus is on an inverted pattern in which the exposed part and the unexposed part of the drawing pattern are reversed. Auxiliary exposure for reducing the influence of the proximity effect by auxiliary exposure with a blurred charged particle beam and making the level of re-exposure due to the backscatter uniform over the entire exposure area (this is called auxiliary exposure) A method called a law is known. A technique for determining the intensity of auxiliary exposure based on the pattern area of each small region is described in Japanese Patent Application Laid-Open No. 5-160010.

[0006]

The principle of the exposure area density method is to draw while correcting the exposure time by using the calculated value of the exposure area density for each small area that changes depending on the drawing position. Therefore, when collectively transferring and drawing a fine pattern of a certain dimension, since each collective transfer pattern is a drawing figure in one small area,
The exposure time in that small area is controlled uniformly. Then, in a small area around the area, a difference between the actual exposure time and the ideal exposure time may occur. This phenomenon is remarkable when the size of the collective transfer pattern is large, and is particularly large in a portion where the exposure area density changes abruptly, causing a problem that the formation size of the fine pattern is different from the desired size.

[0007] In the above-mentioned auxiliary exposure method, auxiliary exposure is performed so that the influence of backscattering becomes uniform, so that such defects in the formed dimensions are reduced. It is necessary to prepare a huge amount of drawing data corresponding to the inversion pattern, and a new apparatus configuration for defocusing and irradiating the charged particle beam is required. There is a problem that the throughput, which is the required time per sheet, is reduced. Further, the auxiliary exposure method has a problem that the mirror body is charged up because the auxiliary exposure is required many times even if the exposure area density is relatively low.

An object of the present invention is to provide an exposure area density method,
An object of the present invention is to provide a charged particle beam lithography apparatus and a pattern forming method which can solve the problems of each of the auxiliary exposure methods and can draw a fine pattern with less influence of a proximity effect.

[0009]

In order to solve the above-mentioned problems, an embodiment of the present invention divides a drawing area into a plurality of small areas having the same area, and calculates the area value of the drawing pattern for each of the small areas. Calculate, correct the calculated area value by weighted addition with the area value calculated for each small area around it, generate an auxiliary exposure figure for the drawing area, and refer to the corrected area value. Auxiliary exposure that calculates the exposure amount of the auxiliary exposure figure generated by the above and irradiates the drawing area on the sample with the exposure amount of the auxiliary exposure figure, and main exposure that irradiates the area of the drawing pattern in the drawing area on the sample It is provided with.

According to another embodiment of the present invention, a computer which divides a pattern to be drawn in advance into a plurality of small areas and calculates an exposure amount for each small area, and a calculated exposure amount for each small area Is configured to have a storage device for storing. For example, this computer calculates the cross-sectional area of the charged particle beam for each drawing pattern by a signal that controls the shape of the charged particle beam while operating only the control circuit of the charged particle beam drawing device in advance before actual drawing, This can be realized by cumulatively adding the cross-sectional area for each small area. The cumulatively added cross-sectional area is
This corresponds to the total exposure amount for each small area, but if the area of each small area is the same and is known, it can be interpreted as a numerical value expressing the exposure area density. In a normal charged particle beam drawing apparatus, a pattern to be drawn is usually decomposed into small exposure figures having no overlap and exposed, so that a correct exposure area density can be calculated at high speed by a simple additional circuit.

When the area density of each small area is calculated,
The numerical value of each small region is smoothed by weighting and averaging processing with the numerical value of the nearby small region in the range where the proximity effect can be obtained. As a result, the difference between the small region and the neighboring small region is corrected to a small value. Modify to be the numerical value of the small area. In this manner, the tendency of the defocused drawing pattern exposed by the backscatter from the substrate is reflected on the corrected exposure area density.

At the time of actual drawing, the position is read from the drawing control circuit for each drawing figure to detect a small area including the figure, and the irradiation time is shortened when the exposure area density of the small area is large. In such a manner, the irradiation time is controlled to be longer at a small place. In areas where the exposure area density is large, excessive exposure is caused by the influence of backscattering.By reducing the exposure time of the drawn figure, an appropriate amount of exposure can be obtained, and the shape change of the figure due to the proximity effect can be reduced. Can compensate.

In addition to reading out the exposure area density of the small area to which the figure to be drawn belongs, the exposure area density of the adjacent small area is also read out, and the exposure area density corresponding to the position of the figure is calculated by interpolation. It can be calculated more precisely. This makes it possible to perform a smoother and more precise proximity effect correction with respect to a change in position.

The above method relates to a conventional exposure area density method and has already been described in the above-mentioned Japanese Patent Application Laid-Open No. 3-225816. In the present invention, this exposure area density method is extended to provide a new auxiliary exposure method as described below. Further, the present invention provides a new writing method using an auxiliary exposure method in combination with the exposure area density method.

The auxiliary exposure method according to the present invention targets the entire pattern region to be drawn in principle. At the beginning,
The pattern area to be drawn is regarded as an auxiliary exposure pattern.
Decomposes into auxiliary exposure figures that can be drawn by multiple exposures. next,
Similar to the exposure area density method, the exposure area density calculated in advance from the drawing pattern is referred to for each auxiliary exposure figure, and if the exposure area density at the position of the auxiliary exposure figure is large, the exposure time is shortened. The auxiliary exposure time is determined so that the exposure time becomes longer when the density is lower.

In this way, a relatively small auxiliary exposure is given where the exposure area density is large and the backscattering exposure is strong, and a strong auxiliary exposure is provided where the exposure area density is small and the backscattering exposure is weak. Is given, the effect of backscattering can be made uniform irrespective of the pattern density, and almost the same effect as the above-described auxiliary exposure method can be realized. In addition, since the exposure area density is smoothed to the exposure area density of a nearby small area, there is no need to defocus and draw the charged particle beam as in the conventional auxiliary exposure method. There is no need to arrange a device for blurring.

That is, according to the present invention, by adopting a new auxiliary exposure method using the exposure area density, compared to the conventional auxiliary exposure method, a new method of exposing the charged particle beam by defocusing is provided. There is no need to provide any means, and there is no need to prepare a large amount of drawing data such as inverted pattern data for auxiliary exposure, so that there is a great effect that the drawing apparatus can be downsized.

The present invention further provides a new drawing method using auxiliary exposure in combination with the exposure area density method, and using auxiliary exposure with a relatively small irradiation amount as an auxiliary to the exposure area density method. When such a combined method is applied, in a region where the exposure area density of a drawn figure changes suddenly, a stronger auxiliary exposure is performed on the side where the exposure area density is lower, so that the optimum irradiation time required in the exposure area density method is required. Changes will be mitigated. As a result, even if a large drawing figure is irradiated by one exposure, the unevenness of the optimum irradiation time inside the figure becomes small, and the deviation of the line width inside the figure from the desired value can be suppressed to a small value. Since it is important to increase the area of the collective irradiation pattern in order to improve the drawing throughput, the effect of the present invention that can draw a large drawing figure with high accuracy is great.

In addition, since the auxiliary exposure can be performed in a shorter irradiation time as compared with the conventional auxiliary exposure method, deterioration of the throughput due to the auxiliary exposure can be avoided, and the possibility of drawing failure due to charge-up of the mirror body can be reduced. Can be reduced. Further, as described above, there is no need to have a large amount of auxiliary exposure designation data corresponding to the reverse pattern of the drawing pattern for the auxiliary exposure, and the practical effect is large.

Further, according to the present invention, even when a lower layer pattern of a different material is already formed on the surface of a sample to be written, optimum proximity effect correction can be provided.
If an underlayer pattern of a different material is present in the sample, the backscattering intensity changes depending on the density of the underlayer pattern during writing, so that the optimal irradiation time of the charged particle beam for correcting the proximity effect changes. Even in such a case, not only the exposure area density of the drawing pattern but also the exposure area density of the lower layer pattern are obtained in advance, and the optimum irradiation time by one or both of the exposure area density method and the auxiliary exposure method is determined. Optimum irradiation time for proximity effect correction can be obtained by determining with reference to the exposure area density of the drawing pattern and the lower layer pattern. In particular, when the lower layer pattern is formed of a heavy metal thin film, the effect of the presence or absence of the lower layer pattern is great, and thus the present invention is highly effective for forming a uniform fine pattern over the entire drawing pattern.

A technique for determining the intensity of the auxiliary exposure based on the pattern area of each small area is described in Japanese Patent Laid-Open No. Hei 5-160010, as described above. There is a means to correct by weighting addition with the area value, etc.Because the distribution of the area value to be referred to already represents the distribution of backscattered energy due to main exposure,
In the auxiliary exposure, there is no need to blur the charged particle beam as in the above-described known technique. In order to correctly irradiate a charged particle beam into a predetermined position by accurately blurring the charged particle beam into a backscattered shape, many correction means are necessary in practice, and the present invention which does not require such blur exposure is practically used. The above advantages are extremely large.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 10 is a longitudinal sectional view showing a configuration of a variable-shaped charged particle beam drawing apparatus using an electron beam as a charged particle beam as an example of an apparatus for carrying out the present invention. In FIG. 10, the portion shown in cross section on the right side is a charged particle beam exposure unit for drawing a wafer, a mask, and a reticle, and is called an electron beam mirror 1000. The surrounding rectangle represents the function of controlling the electron beam mirror 1000 by a block, and the function of the unit having each function is executed by the computer 1012. The sample 1008 is transferred from the transfer unit 1002 to the sample table 1001 inside the electron beam mirror 1000. An electron beam 1004 emitted from an electron gun 1003 at the top of the electron beam body 1000 is shaped by a lens 1006 in the electron beam body 1000, and further comprises a deflector comprising an electromagnetic deflector and an electrostatic deflector. The light is deflected by 1007 and irradiates a target position of a sample 1008 arranged on the sample stage 1001. There are a plurality of types of cross-sectional shapes of the electron beam 1004 to be irradiated, and an arbitrary cross-sectional shape can be transferred onto the sample 1008 by selecting the aperture 1005.

The left part of FIG. 10 shows the functions of the system control by blocks or units, and shares control of the entire system and an external interface. The computer 1012 transmits the pattern data to be drawn held in the hard disk 1021. Frame 1
A block group surrounded by “011” is a control digital processing group that converts the pattern data transmitted from the computer 1012 into electron beam deflection data continuously, in a pipeline, and at high speed. The control unit and the units are connected via a bus 1019 which is a data line, and each processing unit illustrated performs the following processing. (1) Graphic data section 1023: Stores compressed pattern data transmitted from the computer 1012. (2) Graphic restoration unit 1024: Restores the compressed pattern data into graphic data. (3) Graphic decomposing unit 1025: Each restored graphic is replaced with a shot that can be drawn by an electron beam, and data on the position, shape, and exposure of each shot is created. (4) Alignment correction unit 1026: electron beam irradiation position and sample 1
The sensor 1009 monitors the displacement and deformation between the position and the position 008, and performs correction in accordance with the displacement and deformation. (5) Proximity effect correction unit 1027: performs processing for correcting the proximity effect. An exposure map 1029, which is an area map per unit area of a pattern to be drawn in advance, is obtained and stored in a memory, and a process of correcting the exposure in shot units is performed with reference to the value. (6) Follow-up absolute calibration unit 1028: In order to enable continuous writing, the electron beam 1 based on the position of the sample stage 1001 measured by the length measuring unit 1010 and the sample stage position measuring unit 1020.
004 irradiates the target position on the sample 1008,
The electron beam deflection position is calculated and the electron beam mirror 100 is calculated.
The deflection distortion amount of 0 is also corrected. (7) Procedure control unit 1022: Responsible for monitoring and control so that the processing of each unit, that is, the unit, moves smoothly.

The data from the units in the frame 1011 is D / A converted by the D / A converter 1013 and is transferred to the beam controller 1014.
7 is performed. In addition, the high-voltage power supply 1015 generates an acceleration voltage for the electron gun 1003, and the aperture control unit 101
6 controls the aperture exchanging unit 1031 to control the aperture 1
005, the sample stage controller 1017 controls the movement of the sample stage 1001, and the transport system controller 1018 transports the sample 1008 to the sample stage 1001.
Control. Each unit is connected by a bus 1019 which is a data line, and exchanges signals via an interface. The computer 1012 can also control these units.

Next, the principle of the exposure area density method will be described with reference to FIG. FIG. 2 is a graph showing an example of a drawing pattern and an energy amount of exposure by a charged particle beam.
(A) is a figure pattern to be drawn, FIGS. 2 (d) and (g) are examples of a pattern after drawing, and FIGS. 2 (b) (c) (e) (f)
(H), (L) and (N) are graphs showing the amount of energy of exposure by a charged particle beam. As shown in FIG. 2A, it is assumed that there is one thin vertically elongated figure on the left side and five identical figures at narrow intervals from the center to the right side as shown in FIG. Now, the exposure amount of the charged particle beam when this is drawn is a-
As shown in the cross section of a ', if there is no re-exposure due to backscattering from the inner surface of the substrate, only uniform exposure is performed. Therefore, as shown in FIG. Exposed. Therefore, the stored energy level θ
If developed, the figure should be able to be formed into a predetermined shape.

However, in reality, as will be described later, there is re-exposure due to backscattering from the inner surface of the substrate.
As shown in (1), where the exposure area density is large, overexposure occurs. In this case, the stored energy level θ
2 will form a blurred figure as shown in FIG. 2D, and it will be difficult to form a fine figure anymore. This is a phenomenon called a proximity effect.

In the exposure area density method, in order to correct the proximity effect, first, the drawing area is divided into small areas, and the exposure area density in each small area is calculated and smoothed. Smoothing corrects the difference in exposure area density between adjacent small areas between a small area having a maximum value of the exposure area density and a small area having a minimum value, and is also called smoothing. As a result, a waveform having a rough exposure area density is obtained as shown in FIG. Next, when the exposure amount is reduced where the exposure area density of the waveform is high, and the exposure amount is increased where the exposure area density of the waveform is low, the actual stored energy amount is calculated as shown in FIG.
The waveform shown in (f) is obtained. 2F, when development is performed at the stored energy level θ, FIG.
As shown in (g), a graphic pattern having a substantially predetermined line width can be formed.

The problem with the exposure area density method is that, as described above, the optimum exposure amount for each drawing pattern varies greatly depending on the location of the exposure area density, so that exposure can be performed with a single irradiation of a charged particle beam. When the size of a drawn figure becomes large, there is a problem that the dimension of the drawn figure is different from that of a desired drawn figure in a portion where the exposure area density changes abruptly.

As a countermeasure against this, referring to a waveform diagram of the exposure area density shown in FIG. 2E, a small exposure amount is large in a small area having a small exposure area density and a small exposure amount is in a small area having a large exposure area density. An auxiliary exposure is performed before the exposure of the graphic pattern in FIG. That is, when the auxiliary exposure is performed with the waveform of the exposure amount as shown in FIG. 2H and the exposure is performed with the waveform of FIG. 2B, the accumulated energy amount becomes as shown in FIG. In this auxiliary exposure method, as described above, since the auxiliary exposure is performed using a reverse pattern of the exposure amount of the drawing pattern, a pattern requiring an exposure amount of a size as shown in the left end pattern of FIG. Since the exposure amount is reduced as in the pattern at the left end of FIG. 2 (i), as in FIG. 2 (c), a desired width may not be obtained as in the pattern at the left end of FIG. 2 (d). There is.

In order to solve such a problem, the present invention employs an exposure area density method shown in FIGS.
The auxiliary exposure method shown in (h) is used at a fixed ratio. In this case, an energy storage amount having a waveform as shown in FIG. 2 (u) is obtained, and a change in the optimum exposure amount inside the drawn figure can be reduced, so that a change in the pattern dimension can be reduced. In addition, the exposure amount of the pattern at the left end in FIG.

Next, the contents of the present invention will be described more specifically.

As described with reference to FIG. 2, it is an object of the present invention to enable a portion having a small number of patterns and a portion having a large number of patterns to be drawn at the same stored energy level θ. In order to make this possible, the exposure amount of the pattern may be determined such that the median value of the stored energy at the place where the pattern exists and at the place where the pattern does not exist is constant regardless of the pattern density.

FIG. 3 shows an example in which an electron beam is used as a charged particle beam.
8 is a longitudinal section. Consider a case where the electron beam 1004 is irradiated on the photosensitive surface on the sample 1008. The symbols in the figure are
I is the amount of charged particle beam irradiation, E1 is the amount of stored energy on the photosensitive surface due to the irradiation of the charged particle beam, and E2 is the amount of stored energy that the backscattered particles from the sample 1008 return to the photosensitive surface again and give to the photosensitive surface. Further, the ratio of the stored energy amounts of E1 and E2 to the same charged particle beam irradiation energy I is defined as η.

Each pattern to be exposed is minute,
Further, assuming that the exposure area density of the pattern is a constant value p, the amount of stored energy due to backscattering is p
XE2, the stored energy amount U1 in the exposed pattern portion and the stored energy amount U2 in the non-exposed pattern portion
Is represented by the following equation.

U1 = E1 + p × E2 = (1 + p × η) × E1 Equation (1) U2 = p × E2 = p × η × E1 Equation (2) When there is auxiliary exposure, the auxiliary exposure is performed over the entire drawing area. Since the exposure is thin, if the amount of energy stored by the incident particle beam in the auxiliary exposure is E3, the above-mentioned amount of stored energy is respectively expressed by the following equations.

U1 = (1 + p × η) × E1 + (1 + η) × E3 Equation (3) U2 = p × η × E1 + (1 + η) × E3 Equation (4) For actual pattern formation, an exposure pattern Since the intermediate value between the stored energy amount U1 of the portion and the stored energy amount U2 of the non-exposed pattern portion only needs to match the stored energy level θ, the drawing irradiation amount I1 is set so as to satisfy the following expression.
And the auxiliary exposure dose I2 may be determined.

2θ = U1 + U2 = (1 + 2 × p × η) × E1 + 2 × (1 + η) × E3 Expression (5) In order to obtain each dose that satisfies this relationship, first, an appropriate amount satisfying Expression (5) is satisfied. The set of E1 and E3 is determined as follows.

E1 = 2 × θ / [1 + 2 × η × {(1-α) × p + α}] Equation (6) E3 = 2 × θ × {η / (1 + η)} × α × (1-p) / [1 + 2 × η × {(1−α) × p + α}] (7) where α is a new parameter for determining the ratio of auxiliary exposure, and is a positive number smaller than 1. The drawing irradiation amount I1 and the auxiliary exposure irradiation amount I2 correspond to the stored energy amounts E1, E, respectively.
Therefore, when the equations (6) and (7) are rewritten into the equations of the drawing irradiation amount I1 and the auxiliary exposure irradiation amount I2, the following expression is obtained.

I1 = I0 / [1 + 2 × η × {(1-α) × p + α}] Expression (8) I2 = {η / (1 + η)} × I0 × α × (1-p) / [1 + 2 × η × {(1−α) × p + α}] Expression (9) where I1 is the irradiation dose to the drawing pattern portion, and I
Reference numeral 2 denotes an auxiliary exposure irradiation amount, and I0 denotes a charged particle beam irradiation amount for optimally exposing a portion having an exposure area density of 0% without auxiliary exposure.

In the above equation, drawing with α = 0 corresponds to the exposure area density method without auxiliary exposure, drawing with α = 1 results in the auxiliary exposure method, and 0 <α <1 results in two types of irradiation. Is used in combination. Equations (8) and (9) are replaced by equation (5)
Is calculated from the set selected so as to satisfy the following condition. However, by changing the selection method, the ratio between the conventional exposure area density method and the auxiliary exposure method can be freely changed.

Although it is assumed here that the exposure area density p is a constant value that does not depend on the location for simplicity, it is generally a function that changes depending on the location of the drawing pattern.
When the exposure area density p depends on the place, it is necessary to previously smooth p (smoothing) within the range of the backscatter so that p reflects the influence of the backscatter.
Since the smoothed exposure area density p is not significantly affected by spatially small changes, even if the exposure area density p changes spatially, the above-described expression of the dose can be approximately used. On the other hand, the phenomenon in the case where the exposure area density p changes may be modeled in more detail, and the irradiation dose may be calculated more precisely using the exposure area density of a nearby small region.

The proximity effect correction based on the writing pattern density has been described above. As described above, the present invention can be further extended to a method of drawing by correcting not only the influence of the density of the pattern being drawn but also the influence of the density of the lower layer pattern already drawn. Therefore, next, the proximity effect correction in consideration of the influence of the lower layer pattern will be described below.

When a pattern to be drawn is a circuit pattern of a semiconductor wafer, a lower layer pattern may be already formed on a substrate to be drawn, and materials having different properties may be deposited according to the pattern. In such a case, the ratio η of the stored energy amount representing the backscattering ratio is largely different between the region having the lower layer pattern and the region not having the lower layer pattern. In the above-mentioned correction assuming, it is not possible to correct all the areas correctly. However, in such a case, the correction can be similarly performed as described below.

The effect of the presence or absence of the lower layer pattern appears in the ratio η of the amount of stored energy indicating the ratio of the backscattering described above. Assuming that the ratio η of the stored energy amount when there is no lower layer pattern is η0 and the ratio η of the stored energy amount when the lower layer pattern is present on the entire surface is η1, the stored energy amount at a place where the area density of the lower layer pattern is p1 Ratio η
Can be approximated by the following equation by linear interpolation.

Η = η0 + (η1−η0) × p1 Equation (10) Therefore, the ratio η of the stored energy amount is expressed by Equation (8).
By substituting into equation (9) and calculating, it is possible to obtain the optimum particle beam irradiation amount that realizes the proximity effect correction in consideration of the influence of the lower layer pattern. At this time, if α = 0, the two-layer proximity effect correction is performed by the exposure area density method.

The correction of the proximity effect between two layers by the exposure area density method is disclosed in US Pat. No. 5,149,975 by the present inventors, but the present invention provides a new method of correcting the proximity effect between two layers. Is what you do.

In the present invention, the two-layer proximity effect correction combining the auxiliary exposure method and the exposure area density method is performed when α> 0.
For each drawing figure and auxiliary exposure figure, reference is made to the exposure area densities p and p1 at that position, and the irradiation time corrected by Equations (8) and (9) where η of Equation (10) is substituted is used. Exposure. Further, even in the case of only the auxiliary exposure method, the ratio between the drawing figure exposure and the auxiliary exposure is changed to, for example, η1>
In the case of η0, if equations (8) and (9) are redefined and used as in the following equation, the exposure time of the drawn figure becomes constant, and the two-layer proximity effect correction can be realized only by the auxiliary exposure. become.

I1 = I0 / [1 + 2 × η1] Expression (11) I2 = I0 × (η1-η × p) / {(1 + η) × (1 + 2 × η1)} Expression (12) However, the exposure area density p1 of the lower layer pattern also needs to be spatially smoothed in an appropriate backscattering range.

As an actual realizing method, the following equation (1) is used.
(8) and (9)
May be arranged, and new pseudo exposure area densities p2 and p3 satisfying the following equation may be calculated.

I1 = I0 / [1 + 2 × η1 × p2] Equation (13) I2 = {η1 / (1 + η1)} × I0 × α × (1-p3) Equation (14) This calculation has been performed in advance. For example, in each equation, the variable depending on the location is one of the pseudo-exposure area densities p2 and p3. Therefore, during the actual exposure, the pseudo-exposure area densities p2, p2, Alternatively, the pseudo-exposure area density p3 can be read out and converted one-to-one into a particle beam irradiation amount, and the circuit configuration can be simplified.

Next, a specific embodiment of the above-described proximity effect correction processing will be described.

FIG. 1 is a block diagram showing the configuration of the main part of the variable-shaped charged particle beam lithography apparatus described with reference to FIG. The drawing pattern data 3 input from the auxiliary storage device 2 of the control computer 1 is temporarily stored in the high-speed buffer memory 4 and is read at high speed during drawing. Since the read drawing pattern data 3 is usually subjected to a lot of data compression processing, the compressed data is first restored by the restoration circuit 5 into individual basic graphic data. Next, the basic graphic is decomposed in the graphic decomposing circuit 6 into a set of rectangular data having a specific size or less that can be exposed at one time. The output from the figure decomposing circuit 6 includes the particle beam irradiation time T, the vertical and horizontal dimensions (W, H) of the rectangular figure, and the position coordinates (X, Y). In the conventional variable shaping type drawing apparatus which does not need the proximity effect correction function, the irradiation time T is input to the irradiation time generation circuit 7 and converted into the particle beam irradiation / non-irradiation timing signal S2.
The vertical and horizontal dimensions (W, H) are input to a DA converter 8 and converted into an analog signal S3 for forming a particle beam cross section, and the position coordinates (X, Y) are input to a DA converter 9 to be used for position deflection. The signal is converted into an analog signal S4, and is used for controlling the drawing of the charged particle beam mirror unit 10, respectively.

That is, the drawing control circuit of the variable-shaped charged particle beam drawing apparatus shown in FIG. 1 is configured such that each time one rectangular figure is exposed, the position (X, Y) of the rectangular figure, and the vertical and horizontal widths of the rectangular figure (W, H) and time T for irradiating charged particles
Is output as the control data. Proximity effect correction by the conventional exposure area density method is described in JP-A-3-225816 described above.
The proximity effect correction circuit 13 is newly added to the subsequent stage of the graphic decomposition circuit 6 shown in FIG. 1 to calculate the exposure amount for each small area and change the irradiation time for each drawing graphic. Before describing the contents of the present invention, first, the processing contents of the proximity effect correction circuit 13 will be described in detail.

FIG. 4 shows the proximity effect correction circuit 13 shown in FIG.
FIG. 5A shows an example of a drawing figure on a sample surface, and FIG. 5B shows an example of an exposure area density in a storage circuit.

In FIG. 5A, it is assumed that the surface of the sample surface 501 is divided into fifteen small regions 502 as shown in FIG. Each small area 502 includes a drawing figure 503 having a different shape. Each small area 502 is assigned a small area number 504. In FIG. 5B, FIG.
The small area number 504 is assigned to the memory of the storage circuit 23 shown in FIG.

In order to make the explanation easy to understand, the position coordinates X, Y of the position (X, Y) of the above-mentioned rectangular figure are 0 to 1023.
Assume that it takes the value of At this time, X and Y are each 1
It is 2-bit data.

First, an 8-bit numerical value S11 having the upper 4 bits of Y as the upper bits and the upper 4 bits of X as the lower bits is transferred to the memory area indicating the address of the storage circuit 23 via the selection circuit 22 shown in FIG. input. A small area where Y is 0 to 63 and X is 0 to 63 corresponds to address 0 of the storage circuit 23, and a small area where Y is 0 to 63 and X is 64 to 128 is 1 in the storage circuit 23. 64x6, corresponding to the address
The small area divided every four corresponds to one address of the storage circuit 23. Here, FIGS. 5A and 5B
As shown in the figure, the number of this address is the small area number 504. Prior to the exposure operation, it is assumed that "0" is written in all the corresponding small areas of the storage circuit 23.

Next, for each of the rectangular data of the drawing figure to be exposed, the X and Y coordinates are set as addresses of the storage circuit 23, and the W × H value S12 calculated by the multiplier 24 is stored in the storage circuit 23. Is added by the adder 26 to the read content S16 at that address. Then, the data is written to the storage circuit 23 again via the selection circuit 28. That is,
As shown in FIG. 5B, the exposure area density data is stored in the memory 505 for each small area 504. In this way, when the exposure operation of all the exposure data is completed, the sum of the graphic areas of the respective small areas is stored in the storage circuit 23.

Strictly speaking, since the rectangular data may extend over a plurality of small areas, the total sum of the graphic areas cannot be calculated accurately by this method. However, since the size of the rectangle to be exposed is usually sufficiently smaller than the size of the small area, the difference between the total figure area and the actual figure area can be ignored.

In this manner, the exposure area in small area units could be stored in the storage circuit 23. Next, the numerical value of each small area is smoothed using the numerical values of its neighboring small areas, and a macro exposure amount distribution is calculated. One specific method is to replace the numerical value of each small area with a weighted sum of the numerical values of 5 × 5 small areas centered on the small area. In this case, the small area outside the pattern area is calculated on the assumption that the exposure amount is 0.

The intensity of backscattering can usually be approximated by Gaussian weighted smoothing. When the range over which the proximity effect reaches is wide and smoothing over a wider area than the 5 × 5 small area is required, the smoothing processing on the 5 × 5 small area is repeated a plurality of times over a wide range. , The intensity of backscattering is determined. As shown in FIG. 4, such calculations are simply performed by reading the contents of the storage circuit 23, adding weights, and writing the data again. Therefore, the calculation can be performed sufficiently only by adding the calculation circuit 29 to the storage circuit 23. It is.
That is, the address signal S13 corresponding to the desired small area is input from the calculation circuit 29 to the storage circuit 23 via the selection circuit 22, and the smoothing calculation is performed using the output S16 of the storage circuit 23 at that time. S14 is rewritten into the storage circuit 23 via the selection circuit 28.

It is also possible to read the contents of the storage circuit into the control computer of the drawing apparatus without adding a dedicated calculation circuit, and to write the contents into the storage circuit again after the calculation.

When the lower layer pattern of the sample has the proximity effect, by inputting the lower layer pattern data, the exposure area density of the lower layer pattern can be created in the same procedure. FIG. 6 shows a flowchart of a procedure for creating the exposure area density when the lower layer pattern of the sample has the proximity effect.

First, in step 601, three data areas are prepared in the exposure area density storage device, and the data in those areas is cleared to zero. Next, in step 602, pattern data to be drawn is read from the drawing pattern data file 609 and input to the buffer memory. Next, in step 603, the exposure area density of the pattern data to be drawn is created on the first surface of the three surfaces of the exposure area density storage device 610. Next, in step 604, the exposure area density of the first surface is read from the exposure area density storage device 610, corrected by a linear filter so as to reduce the difference in the area density between adjacent small areas, and smoothed. Next, in step 605, the lower layer pattern data is input from the drawing pattern data file 609 to the buffer memory. Next, in step 606, the exposure area density of the lower layer pattern data is created on the second surface. Next, in step 607, the exposure area density of the second surface is smoothed by a linear filter. Next, in step 608, the exposure area densities of the first surface and the second surface are combined to create a final exposure area density on the third surface.
Thus, the exposure area density at the time of the two-layer correction is created.

At the time of actual drawing, the corrected exposure amount of the corresponding small area can be read out from the storage circuit 23 shown in FIG. 4 according to the position coordinates of the rectangular data. And input to the multiplier 33 as the output signal S17 of the selection circuit 34. The multiplier 33 multiplies the irradiation time T, which is the information attached to the rectangular data, by the correction coefficient S17 to obtain new irradiation time data T '. In this embodiment, the multiplier 33 is used to convert the irradiation time. However, if the standard value of the irradiation time is known, the conversion can be made equivalent by addition and subtraction.
Further, the conversion circuit 32a can be realized by a read-only circuit in which an appropriate value is calculated and stored in advance, or is configured by a storage circuit in which a conversion value can be written from outside each time. The contents can also be read using the output signal S16 of 23 as an address. The conversion circuit 32a outputs a small correction coefficient when the exposure amount is large, and outputs a large correction coefficient when the exposure amount is small. In this way, exposure is performed naturally for a short irradiation time in a place where the pattern density is large and the exposure amount is large, and the influence of the proximity effect can be greatly reduced.

FIG. 7 shows a flowchart of a procedure for exposing the drawing pattern data.

First, in step 701, the drawing pattern data is read from the drawing pattern data file 709 and input to the buffer memory. Next, step 70
In step 2, the input graphic data is read from the buffer memory, and in step 703, the graphic data is decomposed into drawing graphic data. Next, in step 704, the exposure area density at the drawing graphic data position is read from the storage device 710. Next, in step 705, the exposure time of the drawing graphic data is corrected using the exposure area density. Next, in step 706, the drawing figure is exposed on the sample surface. Next, in step 707, it is determined whether or not the exposure of all drawing graphic data has been completed. If not completed, the process returns to step 704. If completed, in step 708, whether or not exposure of all input graphic data has been completed. It is determined whether the exposure has not been completed or not, and the process returns to step 702. If the exposure has been completed, the exposure is terminated.

Further, in order to more accurately obtain the exposure amount at the position of the drawing figure, the value of the exposure amount shown in FIG. S16
Is obtained by linear interpolation from the values of the exposure amounts of the surrounding small areas. In this way, the correction of the proximity effect can be performed more finely. Even in this case, the circuit is slightly more complicated than the above-described embodiment, but can be realized without special knowledge.

Although the details of the proximity effect correction circuit 13 in FIG. 1 have been described with reference to FIG. 4, the other parts in FIG. 1 will now be described.

FIG. 2 for the auxiliary exposure employed in the present invention
The auxiliary exposure pattern shown in (h) is a pattern representing the shape of the entire drawing area, but is usually one large rectangular pattern in the deflectable range of the charged particle beam. Of course, a collection of smaller rectangular patterns that cover the entire drawing area may be used depending on the drawing control procedure. The data of the auxiliary exposure pattern is sequentially input to the graphic decomposition circuit 6 by the selection circuit 12, and is decomposed into auxiliary exposure patterns that can be exposed by a single irradiation of the charged particle beam.

As described above with reference to FIG. 4, the exposure area density p at the corresponding position is read out from the storage circuit 23 according to the position data of each of the separated auxiliary exposure figures, and the converted auxiliary exposure figure is converted differently from the drawing figure. The exposure area density p is converted into a correction coefficient by a circuit 32b, and a predetermined irradiation time T is corrected by a multiplier 33 which receives the correction coefficient as an input, and is drawn. The irradiation time T in this case is
Usually, it is a constant value that does not depend on the auxiliary exposure figure.

FIG. 8 shows a flowchart of the procedure of the auxiliary exposure. First, in step 801, the drawing area data is read from the drawing area data file 807 as an auxiliary exposure pattern. Next, in step 802, the auxiliary exposure pattern is decomposed into auxiliary exposure graphic data. Next, in step 803, the exposure area density at the auxiliary exposure graphic data position is read from the storage device 808. Next, step 804
Then, the exposure time of the auxiliary exposure graphic data is corrected using the exposure area density. Next, in step 805, an auxiliary exposure figure is exposed on the sample surface. Next, in step 806, it is determined whether or not the exposure of all the auxiliary exposure graphic data has been completed. If the exposure has not been completed, the process returns to step 803. If completed, the exposure is completed.

The conversion circuits 32a and 3 shown in FIG.
The conversion in 2b is performed according to the above equation (8) when exposing a drawing figure, and according to equation (9) when exposing an auxiliary exposure figure. Here, p is an exposure area density read from the storage circuit, I0 is an exposure amount given in advance, and η and α are constants. Therefore, it can be easily realized by calculating correction data depending on the exposure area density p in advance and storing it as a data table, and reading out a corresponding value in the data table according to the value of the exposure area density p.

The conversion circuits 32a and 3 shown in FIG.
2b is for correction of a drawing figure and auxiliary exposure, respectively.
When α = 1, processing equivalent to the auxiliary exposure method can be realized. At this time, the pattern data for the auxiliary exposure may be a simple small number of rectangular patterns, and the exposure time may be a fixed value. Therefore, there is an advantage that the amount of data to be externally provided for the auxiliary exposure can be extremely small. is there.

Next, a description will be given of a method of obtaining an exposure area density at the time of two-layer correction using auxiliary exposure. In the case of the proximity effect correction taking into account the influence of the lower layer pattern, the exposure area densities p and p1 of the drawing pattern and the lower layer pattern are obtained in advance, and the above-mentioned equations (13) and ( 1
The calculation circuit 29 shown in FIG. 4 calculates the pseudo exposure area densities p2 and p3 satisfying 4). Then, when exposing the drawing figure, the pseudo-exposure area density p2 at that position is read out, the conversion circuit 32a and the multiplier 33 calculate the irradiation amount of the charged particle beam by the above equation (13), and correct the irradiation time. When exposing the auxiliary exposure figure, the pseudo-exposure area density p3 at that position is read out, the conversion circuit 32b and the multiplier 33 calculate the irradiation amount of the charged particle beam by the above equation (14), and correct the irradiation time.

The exposure area density conversion processing to the pseudo exposure area densities p2 and p3 is omitted, and the exposure area densities p and p1 at that position are read out for each exposure, and the above-mentioned equations (11) and (12) are obtained. Can be converted, but the scale of the calculation processing circuit becomes large, so that the pseudo exposure area density p
It is more advantageous to calculate 2, p3.

FIG. 9 is a flowchart showing a procedure for creating an exposure area density at the time of two-layer correction using the auxiliary exposure.
First, in step 901, four data areas are prepared in the exposure area density storage device, and the data in those areas is cleared to zero. Next, in step 902, pattern data to be drawn is read from the drawing pattern data file 910 and input to the buffer memory. Next, step 903
The exposure area density p of the pattern data to be drawn is created on the first surface of the four surfaces of the exposure area density storage device 911. Next, in step 904, the exposure area density storage device 9
The exposure area density p of the first surface is read from 11 and corrected by a linear filter so as to reduce the difference in the area density between adjacent small areas, and smoothing is performed. Next, in step 905, the lower layer pattern data is input from the drawing pattern data file 910 to the buffer memory. next,
In step 906, the exposure area density p of the lower layer pattern data
1 is created on the second surface. Next, in step 907, the exposure area density p1 on the second surface is smoothed by a linear filter. Next, in step 908, the exposure area densities p and p1 of the first surface and the second surface are synthesized, and the pseudo exposure area density p
Create 2. Next, in step 909, the exposure area densities p and p1 of the first surface and the second surface are combined to create a pseudo exposure area density p3 on the fourth surface. Thus, an exposure area density is created.

Note that, first, the auxiliary exposure pattern is exposed for all the drawing areas on the sample surface, and then the main exposure of the drawing pattern is performed for all the drawing areas on the sample surface. Two alignments are required. Therefore, if the exposure of the auxiliary exposure figure and the main exposure of the drawing figure are performed for one area, then the sample is moved, and the exposure of the auxiliary exposure figure and the main exposure of the drawing figure in the next area are performed. Only one alignment is required, saving time.

In particular, when switching between a conventional means for irradiating a charged particle beam defocused for auxiliary exposure processing and a means for drawing, it takes time for each preparation. However, in the auxiliary exposure method according to the present invention, since the auxiliary exposure processing and the drawing graphic exposure processing are switched by the control signal from the control computer, the exposure can be switched at high speed.

Further, if the exposure of the auxiliary exposure pattern and the main exposure of the drawing pattern are performed while moving the sample and deflecting the charged particle beam, the time can be further saved.

Further, since the effect of the exposure of the auxiliary exposure figure and the main exposure of the drawing figure do not change even if the order is changed, even if the main exposure of the drawing figure is performed after the exposure of the auxiliary exposure figure, The main exposure of the drawing figure may be performed before the exposure of the exposure figure.

In the above embodiment, a variable-shaped charged particle beam lithography system having a rectangular cross section has been described. However, a charged particle beam having an arbitrary cross-sectional shape such as a triangular shape or an L-shaped shape may be used. Is also good. Since the drawing apparatus includes a numerical signal for controlling the shape thereof, it is possible to calculate the cross-sectional area of the drawing apparatus by a calculation circuit. There is no hindrance to the implementation.

When the present invention is applied to a drawing apparatus having a function of repeatedly forming a pattern by selecting the shape of a specific circuit pattern and using the selected pattern as an aperture for variable shaping, it is necessary to cut off the specific pattern. Since the area is known in advance, the area may be used as a parameter, and the exposure area density corresponding to each parameter may be cumulatively added.

In the embodiment of the present invention, the exposure area density and the pseudo-exposure area density are calculated by a computer provided inside the drawing apparatus. May be transmitted to the drawing apparatus prior to the writing.

Further, in the embodiment of the present invention, the drawn figure is collectively exposed by a single irradiation of the charged particle beam passing through the aperture of the specific shape. However, the aperture is larger than the cross-sectional area of the charged particle beam, The case where the particle beam scans the aperture for exposure may be used.

With the above configuration, it is possible to realize the proximity effect correction more easily and more accurately than in the past, and to form an extremely fine pattern using charged particle beams.

The proximity effect correction using the auxiliary exposure method according to the present invention does not require a large amount of auxiliary exposure pattern data and exposure time data for auxiliary exposure, and specially performs exposure by defocusing a charged particle beam. Since the above device configuration is not required, the size of the drawing device can be reduced.

In the proximity effect correction using the auxiliary exposure method of the present invention, it is possible to perform two-layer correction in consideration of the influence of the lower layer pattern, which is difficult with the conventional auxiliary exposure method. If there is a wiring pattern made of heavy metal with a high reflectance of charged particle beams in the lower layer, the correction amount of the proximity effect changes on the wiring pattern and elsewhere, making it difficult to form a fine pattern simultaneously in all places However, this can be achieved by using the auxiliary exposure method of the present invention. This is particularly effective when an ultrafine circuit pattern on a semiconductor wafer is formed by directly drawing with a charged particle beam.

The drawing method combining the exposure area density method and the auxiliary exposure method according to the present invention, when the area that can be exposed by a single irradiation of the charged particle beam becomes large, requires a simple exposure area density method. This has the effect of reducing the slight shift that occurs in the line width of the exposure pattern in the portion where the density changes rapidly. That is, it is possible to draw a large figure at once with the same line width accuracy, and the drawing throughput is improved.

Further, according to the present invention, it is possible to perform drawing with higher accuracy as compared with the conventional charged particle beam drawing method.
An extremely fine semiconductor pattern can be formed.

(Supplementary Note) When exposing a drawing pattern on a sample by irradiation with a charged particle beam, a pattern forming method comprising: a main exposure step of irradiating a pattern portion on the sample; and an auxiliary exposure step of an entire exposure area of a drawing area on the sample. The step of auxiliary exposure of the entire drawing area, dividing the drawing area into a plurality of small areas having the same area, and calculating an area value for irradiating the charged particle beam for each of the small areas; and Correcting the calculated area value by weighted addition with the area value of the peripheral small area calculated for each small area, and generating a plurality of auxiliary exposure figures for the entire drawing area And a step of determining an exposure amount of the generated auxiliary exposure pattern with reference to the corrected area value.

2. The entire pattern area to be drawn is targeted, and the pattern area to be drawn is considered as an auxiliary exposure pattern, and it is decomposed into auxiliary exposure figures that can be drawn by one exposure,
Similar to the exposure area density method, the area density calculated in advance from the drawing pattern is referred to for each auxiliary exposure figure, and if the area density at the position of the auxiliary exposure figure is large, the exposure time is shortened. A pattern forming method, wherein the auxiliary exposure time is determined so that the exposure time becomes longer.

3. Further, a pattern forming method is characterized in that auxiliary exposure is used in combination with the exposure area density method, and auxiliary exposure with a relatively small irradiation amount is used as an auxiliary to the exposure area density method.

[0095]

As described above, according to the present invention, the problems of the exposure area density method and the auxiliary exposure method can be solved and a fine particle pattern can be drawn with less influence of the proximity effect. And a method for forming a pattern.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a variable-shaped charged particle beam drawing apparatus.

FIG. 2 is a diagram illustrating an example of a drawing pattern and a graph illustrating an energy amount of exposure by a charged particle beam.

FIG. 3 is a longitudinal sectional view of a sample irradiated with an electron beam.

FIG. 4 is a functional block diagram of a proximity effect correction circuit.

FIG. 5 is an explanatory diagram showing an example of a drawing figure on a sample surface and an example of an exposure area density in a storage circuit.

FIG. 6 is a flowchart illustrating a procedure for creating an exposure area density when a lower layer pattern of a sample has a proximity effect.

FIG. 7 is a flowchart showing a procedure for exposing drawing pattern data.

FIG. 8 is a flowchart illustrating a procedure of auxiliary exposure.

FIG. 9 is a flowchart showing a procedure for creating an exposure area density at the time of two-layer correction using auxiliary exposure.

FIG. 10 is a longitudinal sectional view showing a configuration of a variable-shaped charged particle beam drawing apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Control computer, 2 ... Auxiliary storage device, 3 ... Drawing pattern data, 4 ... Buffer memory, 5 ... Restoration circuit, 6 ... Graphic decomposition circuit, 7 ... Irradiation time generation circuit, 11 ... Auxiliary exposure pattern generation circuit, 12 , 22 ... selection circuit, 13 ... proximity effect correction circuit, 23 ... memory circuit, 1004 ... electron beam, 10
08: sample, 1012: computer, 1027: proximity effect correction unit, 1029: exposure map.

Claims (15)

[Claims] 1. A pattern forming method for exposing a drawing pattern on a drawing area on a sample by irradiation of a charged particle beam,
An auxiliary exposure step of irradiating a drawing region on the sample with the charged particle beam, and a main exposure step of irradiating a region of a drawing pattern in the drawing region on the sample with the charged particle beam; Dividing the drawing area into a plurality of small areas having the same area, calculating the area value of the drawing pattern for each small area, and calculating the calculated area value for each small area around the drawing pattern. Correcting by a weighted addition with the corrected area value, generating an auxiliary exposure graphic for the drawing area, and calculating an exposure amount of the generated auxiliary exposure graphic with reference to the corrected area value. A pattern forming method, comprising: 2. The method according to claim 1, wherein the auxiliary exposure step calculates an area value of a lower layer pattern formed on the sample for each of the small areas, and calculates an area value of the lower layer pattern for each of the small areas. Correcting the area value of the lower layer pattern of the small area around the area calculated for each area, calculating the exposure amount of the generated auxiliary exposure figure,
A step of calculating the exposure amount with reference to the corrected area value and the corrected area value of the lower layer pattern. 3. The pattern forming method according to claim 1, wherein said auxiliary exposure step is performed before said main exposure step. 4. The pattern forming method according to claim 1, wherein said auxiliary exposure step is performed after said main exposure step. 5. A charged particle beam drawing apparatus for exposing a drawing pattern on a drawing area on a sample by irradiation with a charged particle beam, comprising: an auxiliary exposure for irradiating a drawing area on the sample with the charged particle beam; A charged particle beam exposure unit for performing a main exposure of irradiating the region of the drawing pattern in the drawing region with the charged particle beam, connected to the charged particle beam exposure unit via a data line, and making the drawing regions equal in area It is divided into a plurality of small areas, the area value of the drawing pattern is calculated for each small area, and the calculated area value is corrected by weighted addition with the area value calculated for each small area around the small area. Calculating a main exposure amount for each small area of the sample by the charged particle beam exposure unit, generating an auxiliary exposure figure for the drawing area, and referring to the corrected area value, A calculator that calculates an auxiliary exposure amount for exposing the drawing area with the generated auxiliary exposure figure, and transmits the calculated auxiliary exposure amount and the main exposure amount to the charged particle beam exposure unit. Charged particle beam drawing equipment. 6. The charged particle beam drawing apparatus according to claim 5, further comprising a memory for storing the area value corrected by the computer. 7. The charged particle beam exposure unit according to claim 5, wherein the charged particle beam exposure unit performs an electric deflectable area of the charged particle beam after an auxiliary exposure based on the auxiliary exposure amount calculated by the exposure amount calculation unit. A charged particle beam lithography apparatus for performing main exposure for irradiating each smaller area. 8. The charged particle beam lithography apparatus according to claim 5, further comprising a sample stage on which the sample is placed and moved after the auxiliary exposure and the main exposure by the charged particle beam exposure unit. . 9. The charged particle beam lithography apparatus according to claim 5, further comprising a sample stage on which the sample is placed and moved together with the auxiliary exposure and the main exposure by the charged particle beam exposure unit. 10. The computer according to claim 5, wherein the calculator calculates an area value of a lower layer pattern formed on the sample for each of the small regions, and calculates the calculated area value of the lower layer pattern in the vicinity thereof. Correcting the area value of the lower layer pattern calculated for each of the small areas, and determining the exposure amount of the auxiliary exposure pattern with reference to the corrected area value and the corrected area value of the lower layer pattern. A charged particle beam drawing apparatus characterized by the above-mentioned. 11. A charged particle beam drawing apparatus for exposing a drawing pattern on a drawing area on a sample by irradiation with a charged particle beam, comprising: an auxiliary exposure for irradiating a drawing area on the sample with the charged particle beam; A charged particle beam exposure unit for performing a main exposure of irradiating a region of a drawing pattern in the drawing region with the charged particle beam, the drawing region is divided into a plurality of small regions having the same area, and for each of the small regions, An area calculation unit for calculating the area value of the drawing pattern, an area correction unit for correcting the calculated area value by weighting and adding the area value of a small area around the small area, and storing the corrected area value A storage device, a main exposure amount calculation unit that calculates an exposure amount for each of the small regions based on the area value corrected by the area correction unit, A graphic generating unit for generating an auxiliary exposure graphic, and calculating an auxiliary exposure amount for exposing the drawing area with the auxiliary exposure graphic generated by the graphic generating unit with reference to the corrected area value stored in the memory An auxiliary exposure calculation unit, a main exposure calculation unit and an auxiliary exposure calculation unit connected to the charged particle beam exposure unit, and a data line for transmitting the exposure for each small area and the auxiliary exposure. A charged particle beam drawing apparatus characterized by the above-mentioned. 12. A pattern forming method for exposing a drawing pattern on a drawing region on a sample by irradiation of a charged particle beam, wherein the region of the drawing pattern to be exposed is divided into a plurality of small regions, and the small region is divided into a plurality of small regions. Calculating the area value of the drawing pattern, correcting the calculated area value by weighted addition with the area value calculated for each small area around the calculated area value, and correcting the calculated area value based on the corrected area value. Calculating an exposure amount for each small area, generating an auxiliary exposure figure for the drawing area, and an auxiliary exposure amount for the charged particle beam of the generated auxiliary exposure figure based on the corrected area value Calculating the auxiliary exposure amount of the drawing area based on the calculated auxiliary exposure amount, and performing the writing on the sample based on the calculated exposure amount for each of the small regions. Pattern forming method characterized in that it comprises a main exposure step of irradiating the region of the turn in the charged particle beam. 13. A charged particle beam drawing apparatus for exposing a drawing pattern on a drawing area on a sample by irradiation with a charged particle beam, comprising: an auxiliary exposure for irradiating a drawing area on the sample with the charged particle beam; A charged particle beam exposure unit for performing a main exposure of irradiating the region of the drawing pattern in the drawing region with the charged particle beam, dividing the drawing region on the sample, and a drawing pattern region for each of the divided small regions; An exposure ratio calculation for calculating an area ratio with a non-drawing pattern region, and for a small region having a relatively small area ratio, a small exposure region for the auxiliary exposure and a large exposure region for the main exposure for a large region. A charged particle beam drawing apparatus comprising: a unit; 14. A charged particle beam lithography apparatus according to claim 13, wherein said charged particle beam exposure unit performs said main exposure after said auxiliary exposure. 15. A charged particle beam lithography apparatus according to claim 13, wherein said charged particle beam exposure unit performs said main exposure before said auxiliary exposure.