JPH04242919A - Charged beam drawing apparatus - Google Patents

Abstract

PURPOSE:To enable drawing accuracy of a fine pattern to be improved by calculating an angle between reference coordinates of drawing and an angle which is formed in reference to an edge of a forming beam and then rotating and moving a forming aperture or the forming beam so that this angle is equal to 0. CONSTITUTION:By scanning a fine dot-shaped mark which is provided on a sample surface 18 with a forming beam, an intensity distribution at the edge part of the beam is measured in two directions, namely x and y. The measured beam intensity distribution is expressed within a three-dimensional space, namely reference coordinates (x, y) of drawing and z axis of beam intensity distribution, and an equation of the plane which is in contact with the edge portion of the forming beam is obtained. An angle theta formed by the reference coordinates of drawing and the edge of the forming beam is calculated from this equation and forming apertures 13a and 15a or the forming beam are rotated and moved so that the angle theta is equal to 0.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable shaped beam type charged beam drawing apparatus, and more particularly to a charged beam drawing apparatus having a function of correcting rotational deviation of a shaped beam.

0002

2. Description of the Related Art In recent years, variable shaping beam type electron beam writing apparatuses have been developed in which the dimensions of the beam can be arbitrarily changed to form desired patterns on samples such as semiconductor wafers and mask substrates. A variable shaping beam type electron beam lithography system uses a first
An aperture mask is irradiated with an electron beam, and the beam that has passed through the shaping aperture of this mask is imaged onto a second aperture mask having a rectangular aperture, and the beam is deflected between each mask to improve the optics of the shaping aperture. The beam size can be varied by changing the overlap of the targets.

By the way, in order to write a fine LSI pattern on a sample surface using this type of variable shaped beam method, it is necessary to determine the direction of the edge of the shaped beam with high precision. As a beam edge correction method, Japanese Patent Application Laid-Open No. 62-4319
No. Publication is known. This detects the beam intensity distribution at each end of the two sides when the two sides corresponding to the aperture edges of the first and second shaping apertures, which should be parallel to each other on the sample surface, are brought close together. However, in this method, the direction deviation of the first and second shaping apertures is corrected so that these beam intensities become the same. FIG. 6 shows a beam shaped by the above method and the corresponding beam intensity distribution.

However, this type of device has the following problems. That is, as is clear from FIG. 6, which of the first and second molding apertures is
It is not possible to quantitatively measure in which direction it is rotating. For this reason, it has been difficult to easily correct the rotational deviation of the shaped beam with high precision.

[0005]

[Problems to be Solved by the Invention] As described above, in the conventional charged beam writing apparatus using the variable shaped beam method, it is not possible to easily correct the rotational deviation of the shaped beam with high precision, and this problem occurs when forming fine patterns. This was a factor that led to a decrease in drawing accuracy.

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to easily correct the rotational deviation of a shaped beam with high precision, and to improve the drawing accuracy of fine patterns. The object of the present invention is to provide a charged beam lithography device that can contribute to the present invention.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention forms a shaped beam by optically overlapping shaping apertures that are optically spaced apart, and irradiates this shaped beam onto a sample surface. In a charged beam lithography system that draws a desired pattern using a shaped beam, a shaped beam scans a minute dot-like mark provided on a sample surface to measure the intensity distribution at the edge of the beam. is measured in multiple directions or at three or more different positions, and these beam intensity distributions are calculated based on the drawing reference coordinates (x, y
) is expressed in a three-dimensional space by adding the z-axis of the beam intensity distribution, find the equation of a plane that touches or approximates the edge portion of the shaped beam, and from the equation of this plane, the reference coordinates for drawing and the shaped beam The angle formed with the edge of the beam is calculated, and the shaping aperture or beam is rotated so that this angle becomes zero.

[0008]

[Operation] According to the present invention, the drawing reference coordinates (x, y) are determined by measuring the beam intensity distribution at the edge portion of the shaped beam in a plurality of different directions or at three or more different positions.
It is possible to find the equation of a plane that is tangent to or approximates the edge portion of the shaped beam, which is represented in a three-dimensional space including the z-axis and the z-axis representing the beam intensity. Therefore, by geometrically calculating the angle (edge rotation angle) between the plane expressed by this equation and the drawing reference coordinates, and rotating the shaping aperture corresponding to the edge by this angle, the edge It becomes possible to easily set the direction parallel to the drawing reference coordinates with high accuracy.

[0009] Furthermore, if there is dust or the like near a minute mark on the sample surface, the intensity distribution of the detected beam may become non-uniform. To avoid this, shortening the beam size in the direction perpendicular to the beam scanning direction and correcting non-uniformity will improve the accuracy of direction detection of the edge of the shaped beam. becomes possible.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing an electron beam lithography apparatus according to an embodiment of the present invention. An electron beam emitted from an electron gun (charged beam source) 11 is uniformly irradiated onto a first aperture mask 13 by a focusing lens 12 . The beam that has passed through the shaping aperture 13a of the aperture mask 13 is imaged onto the second aperture mask 15 by the projection lens 14. Aperture mask 15
The beam that is shaped after passing through the shaping aperture 15a is directed to the sample surface 18 by the reduction lens 16 and the objective lens 17.
imaged on top.

A scanning deflector 1 is provided between the lenses 16 and 17.
9 is arranged, and the beam position on the sample surface 18 is changed by this deflector 19. First aperture mask 13
A blanking deflector 20 and a shaping deflector 21 are arranged between the lens 14 and the lens 14 . Then, the timing of beam irradiation is controlled by the blanking deflector 20. Furthermore, by changing the beam position imaged on the aperture mask 15 by the shaping deflector 21,
The dimensions of the shaped beam are varied.

The deflectors 19, 20, 21 include a computer 30.
A predetermined deflection signal is supplied from the interface 32 through the interface 32 . That is, each deflection voltage is controlled by the computer 30 according to the pattern data in the memory 31, and a predetermined deflection voltage is applied to each deflector 19, 20, 21, respectively.

On the other hand, above the sample surface 18, a backscattered electron detector 41 for detecting backscattered electrons is arranged. The detection signal of this detector 41 is sent to a monitor 43 via an amplifier 42.
It is also supplied to the computer 30 via the A/D converter 44. In addition, aperture masks 13 and 15
is a drive mechanism 45, 4 consisting of a rotary motor, a piezoelectric element, etc.
6, it has a rotatable structure. Then, the computer 30 determines the amount of directional deviation of the shaped beam based on the backscattered electron signal, and adjusts the direction of the aperture masks 13 and 15 according to this amount of deviation.
is used to control the rotation. Next, a method for correcting the direction (rotational deviation) of a shaped beam using the above device will be described.

Correction of the direction of a shaped beam is to make the four sides of the shaped beam (rectangle) coincide with reference coordinates for drawing (hereinafter referred to as drawing coordinates). FIG. 2(a) shows the shaped beam on the sample surface, and FIG. 2(b) shows the image of the first shaping aperture 13a and the second shaping aperture when forming the shaped beam.
The positional relationship of the molding aperture 15a is shown. Here, Figure 2
Sides j' and k' of the shaped beam 51 shown in (a) are images of sides j and k shown in (b), respectively. Therefore, if the direction of the j' side is misaligned, the direction misalignment of the j' side can be corrected by rotating the second shaping aperture 15a (j side) by the amount of the misalignment. Hereinafter, the direction correction of the j' side shown in FIG. 2(a) will be explained as an example.

First, a method for measuring the beam intensity distribution on the j' side by the gold particles 52 will be explained using the beam 51 shown in FIG. 2(a). When the shaped beam 51 is scanned in the direction of the arrow by the deflector 19, electrons corresponding to the intensity of the beam are reflected from the portion of the beam projected onto the sample surface 18 that overlaps with the gold particles 52. By detecting these reflected electrons with the detector 41, the beam intensity distribution on the dotted line can be measured.

However, at this time, reflected electrons from the sample surface 18 also enter the detector 41. In addition to gold particles, there may be dust or very small pieces of gold particles on the sample surface 18, and in order to obtain an accurate beam intensity distribution, it is necessary to minimize the probability of being affected by these particles. To this end, the beam intensity distribution may be obtained by shortening the beam dimension in the direction perpendicular to the beam scanning direction.

Next, the positional relationship of beam scanning for beam intensity distribution measurement, which is necessary to calculate the direction deviation angle of the j'' side, will be explained using FIG. 3. (x, y), the two-dimensional map (contour lines) of the beam intensity distribution, and the beam scanning directions A, B, and C. Find j
The "side direction deviation" is the angle θ between the "j" side and the drawing coordinate axis (x). 53 is the center of the shaped beam.

First, in the C direction (direction parallel to y) in FIG.
The beam was scanned to detect reflected electrons from the gold particles.
Obtain the beam intensity distribution as shown in (c). From this, determine the y position of edge j'', and scan the beam in the A direction (parallel to x) in Figure 3 while slightly shifting the position in the y direction around this area.At this time, the beam reflected from the gold particle The obtained electrons are detected and an intensity distribution as shown in FIG. 4(a) is obtained.

[0020] Here, in order to find the direction of the beam,
It is sufficient to scan the beam once in the A direction to capture the intensity distribution, but in this example, to improve accuracy, beam scans are performed multiple times and the waveform closest to the 50% level 59 of the intensity distribution is extracted. Used for beam direction detection. At the same time, the beam is scanned on a dotted line B that is parallel to the drawing coordinate axis x and passes through the center Q of the shaped beam, and the beam intensity distribution as shown in FIG. 4(b) is also measured. Next, a method of calculating the direction deviation angle θ of the j'' side by processing these beam intensity distributions with the computer 30 will be described.

First, the center level 59 of the beam intensity (=(maximum beam intensity-minimum beam intensity)/2) is calculated from the beam intensity distribution shown in FIG. 4(b). Next, Figure 4
Select the waveform closest to level 59 among the multiple beam intensity distribution waveforms shown in FIG.
8 (z=m1 y+c1). Here, the regression line is a straight line that approximates the part corresponding to the j'' side of the waveform closest to the intensity distribution 50% level 59 described above.Next, the drawing of the j'' side shown in FIG. 4(c) From the beam intensity distribution in the coordinate axis y direction, a regression line 55 is drawn in the same manner as above.
Find (z=m0 x+c0).

FIG. 5 is a three-dimensional representation of the intensity distribution of the shaped beam shown in FIG. 3 by adding the z-axis representing the beam intensity to the drawing coordinates (x, y). Here, the surface 62 is j
Furthermore, the angle θ formed between the drawing coordinate (x) and the straight line 61 formed where the surface 62 intersects with the z=0 plane is the direction deviation angle of the "j" side. By the way, the previously determined regression lines 55 and 58 are straight lines on the surface 62. Therefore, if the equation of the plane determined by the two straight lines 55 and 58 is expressed as ax+by+cz=1, then the straight line that intersects on the XY plane is y=(-a/b
)x+1/b, and when converted to the inclination angle of the straight line, θ=tan-1
(-a/b). Furthermore, when the straight lines obtained in FIGS. 4(a) and 4(c) are expressed in a three-dimensional space, z=m0 y+c0 z=m1 x+c1. The relationships between the above plane equations are as follows. a=-cm1 b=-cm0 Therefore, the direction of the beam is expressed by the following equation. θ=tan-1(-m1/m0)

[0023] If the molding aperture forming the j" side is rotated by the direction deviation angle θ of the j" side obtained in this way, the direction deviation of the j" side is corrected. Note that k"
The direction deviation angle of the sides can also be found in the same way. Furthermore, similarly measure the deviation angle of the side opposite to j", k",
It is also possible to perform correction with higher precision. Further, in order to rotate the aperture masks 13 and 15, the drive mechanism 4
5, 46 or an external manual rotation introducing machine.

According to this embodiment, the intensity distribution shown in FIG. 4(a) obtained by scanning the shaped beam in the measurement edge direction (A) and the intensity distribution obtained by scanning in the direction (C) perpendicular to this Based on the intensity distribution shown in Figure 4(c), the z-axis representing the beam intensity is added to the drawing reference coordinates (x, y).
The equation of the plane tangent to the edge portion of the shaped beam, represented in dimensional space, can be determined. Then, by geometrically calculating the angle (edge rotation angle) between the plane expressed by this equation and the drawing reference coordinates, and rotating the molding aperture corresponding to the edge by this angle, the edge It is possible to make the direction parallel to the drawing reference coordinates. Thereby, the rotational deviation of the shaped beam can be easily corrected with high precision, and the drawing precision of fine patterns can be improved.

It should be noted that the present invention is not limited to the above-mentioned embodiments. In the example, the intensity distribution on the side of the shaped beam was measured parallel to the drawing coordinates (x, y), and the direction deviation angle of the side was calculated from the measurement results. is uniquely determined, so the surface 62 can be approximated by a plane determined from the beam intensity at three points on the side of the shaped beam or a regression plane calculated from the beam intensity distribution at three or more points on the side. The beam side misdirection can be calculated.

In addition, if there is dust or very small pieces of gold particles on the sample surface in addition to the gold particles, as shown in FIG. 4(b),
), the beam intensity distribution becomes non-uniform due to these influences. At this time, similarly, the slope of the regression line 58 (
m1) must be corrected because it is affected by the above. Therefore, in the beam intensity distribution shown in FIG. 4(b), the regression line 60 is
Find (z=m2 x+c2). Then, the slope just before regression obtained when scanning the j” side in the x direction is corrected (m1 − m2). The direction of the beam in this case is expressed by the following formula: θ=tan−1(−(m1 − m2)/m0) Then, by correcting the direction of the aperture by shifting the direction by this θ, it becomes possible to write a fine pattern with a shaped beam.

Furthermore, in the embodiment, the shaping aperture is rotated to correct the rotational deviation of the beam, but instead of this, the beam itself may be rotated by changing the excitation current of the electron lens. However, in this case, the imaging position of the beam also changes, so the sample stage is moved in the vertical direction.

Furthermore, the present invention is applicable not only to electron beam lithography apparatuses but also to ion beam lithography apparatuses. Furthermore, the present invention can be similarly applied not only to charged beam exposure apparatuses but also to exposure apparatuses that use light, and not only to exposure apparatuses but also to various apparatuses that use shaped beams. In addition, various modifications can be made without departing from the gist of the present invention.

[0029]

As described in detail above, according to the present invention, the intensity distribution of the edge portion of the beam is measured in a plurality of different directions or at three or more different positions, and a predetermined plane equation is calculated from these beam intensity distributions. The rotational deviation of the shaped beam can be corrected by calculating the angle between the drawing reference coordinates and the edge of the shaped beam from this plane equation, and rotating the shaping aperture or shaped beam so that this angle becomes zero. It can be corrected with high precision and easily. Therefore, it is possible to contribute to improving the drawing precision of fine patterns.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an electron beam lithography apparatus used in a method according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a method for measuring the intensity distribution of a shaped beam and the shape of the shaped beam.

FIG. 3 is a schematic diagram showing positions at which the beam intensity distribution of a shaped beam is measured.

FIG. 4 is a schematic diagram showing beam intensity distribution measurement results at measurement positions A to C shown in FIG. 3;

FIG. 5 is a schematic diagram three-dimensionally showing the intensity distribution of a shaped beam.

FIG. 6 is a schematic diagram showing the relationship between beam shape and backscattered electron signal profile.

[Explanation of symbols]

11...electron gun, 12...focusing lens, 13...first
aperture mask, 13a, 15a...molded aperture, 14...projection lens, 15...second aperture mask, 16...reduction lens,
17... Objective lens, 18... Sample surface, 19... Scanning deflector, 20... Blanking deflector, 21... Shaping deflector, 30... Computer, 31... Memory, 32... Interface, 41... Backscattered electron detector, 45, 46... Drive mechanism, 51... Shaped beam,
52... Gold particle, 53... Center of shaped beam, 55, 58, 60... Regression line, 57... Center of waveform, 59... Center level of beam intensity, 62... Surface representing j side.

Claims (3)

[Claims] 1. A charged beam drawing device that forms a shaped beam by optically overlapping shaping apertures that are optically spaced apart, and irradiates the shaped beam onto a sample surface to draw a desired pattern. Measure the intensity distribution of the edge portion of the beam by scanning a minute dot-like mark provided on the shaped beam with the shaped beam, and measure the beam intensity distribution of the edge portion in multiple different directions or at three or more different positions. and a means for setting the beam intensity distribution measured by the means to the reference coordinates (x, y) of the drawing.
Means for obtaining an equation of a plane expressed in a three-dimensional space including an axis and touching or approximating the edge portion of the shaped beam; and a drawing reference coordinate and the shaped beam from the equation obtained by the means. A charged beam lithography apparatus comprising means for calculating an angle between the shaped aperture or the shaped beam and an edge thereof, and rotationally moving the shaped aperture or the shaped beam so that this angle becomes zero. 2. The charged beam lithography apparatus according to claim 1, wherein when measuring the beam intensity distribution at an edge portion of the shaped beam, the shaped beam size in a direction perpendicular to the edge portion is shortened. 3. The beam intensity distribution at the center of the shaped beam is measured to determine the non-uniformity of the beam intensity distribution, and based on this, the beam intensity distribution at the edge portion of the shaped beam is corrected. A charged beam lithography apparatus according to claim 1, characterized in that: