JPH11176720A - Electron ream exposure device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron beam exposure device capable correcting proximity effect without deteriorating the throughput, reduces blurs due to Coulomb effect, is easily to execute beam adjustment work, and the beam position of which is stable. SOLUTION: An aperture 18 is provided for a crossover position 19 on the upstream side from a mask 14. An opening angle at forming of an image of the mask 14 on a wafer 17 is determined by the aperture 18. Scattered electrons 23 and 24 generated from a part except for the pattern of the mask 14 pass through a transfer lens 15, and the end parts of then are cut by an aperture 21. They are image-formed on the wafer 17 with the opening angle decided by the size of the aperture 21. Since the opening angle of the scattered electrons 23 and 24 is several times as much as the opening angle of the electron beam 22 which passes through the pattern part of the mask 14, an image accompanied with blurs is obtained and makes accumulated energy distribution in resist on the wafer 17 flat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam exposure apparatus used mainly for lithography of semiconductor integrated circuits and the like.

[0002]

2. Description of the Related Art In recent years, electron beam exposure apparatuses having both high resolution of exposure and high throughput have been developed. A method conventionally developed for this purpose is a batch transfer method. This is a method of exposing one die (one chip) or a plurality of dies at a time. However, in this method,
Recently, there are problems such as difficulty in manufacturing a mask serving as a master for transfer, and difficulty in reducing aberration to a required degree in a large optical field such as one or more dies. The development of this device is declining.

[0003] In recent years, a method which has been frequently studied is that, instead of exposing one or a plurality of dies at a time, an exposure apparatus having a large optical field is used and divided into small areas for transfer exposure. It is. This method is called a division transfer method. In the division transfer method, exposure is performed for each of the small areas while correcting aberrations such as the focal point of the image of the small area formed on the surface to be exposed and the field distortion. As a result, it is possible to perform exposure with higher resolution and higher accuracy in correcting distortion of the optical system over an optically wider area than batch transfer.

FIG. 2 shows an outline of the division transfer system. In FIG. 2, 100 is a mask, 100a is a small area on the mask 100, 100b is a boundary area between the small areas 100a, 11
0 is a sensitive substrate such as a wafer coated with a resist, 110a
Is an area for one die (one chip) of the sensitive substrate 110, 11
0b is the sensitive substrate 11 corresponding to each of the small areas 100a.
0, AX is the optical axis of the charged particle beam optical system, EB
Is a charged particle beam, and CO is a crossover point of the charged particle optical system.

[0005] On the mask 100, a large number of small areas 100a each having a pattern to be transferred to the sensitive substrate 110 on the membrane are formed in a boundary area 1 where no pattern exists.
00b. A grid-like column is provided at a portion corresponding to the boundary region 100b to protect the membrane from heat and strength.

[0006] Each of the small areas 100a is one of the sensitive substrates 110.
The pattern to be transferred to the die area 110a is provided with each divided partial pattern, and the divided partial pattern is transferred to the sensitive substrate 110 for each divided pattern. Sensitive substrate 110
2B has the appearance as shown in FIG.
In FIG. 2A, a part of the sensitive substrate 110 (FIG. 2B)
Va section of FIG. 2 is shown in an enlarged manner.

In FIG. 2, the optical axis A of the charged particle beam optical system is shown.
The z-axis is set in parallel with X, and the x-axis and y-axis are set in parallel with the arrangement direction of the small areas 100a. Then, as shown by arrows Fm and Fw, the charged particle beam is scanned stepwise in the y-axis direction while continuously moving the mask 100 and the sensitive substrate 110 in the x-axis direction in opposite directions, thereby forming a row of small regions 100a. Are sequentially transferred, and after the pattern transfer of the row is completed, the next row of the small area 100a adjacent in the x-axis direction is scanned with the charged particle beam, and thereafter, the transfer (division) is performed similarly for each small area 100a. Is repeated to transfer a pattern for one die (one chip).

At this time, the scanning order of the small area 100a and the transfer order to the sensitive substrate 110 are indicated by arrows Am and A, respectively.
As shown by w. The reason why the continuous movement directions of the mask 100 and the sensitive substrate 110 are opposite is that the x-axis and the y-axis of the mask 100 and the sensitive substrate 110 are inverted by the pair of projection lenses.

In the case of performing transfer (split transfer) in such a procedure, simply projecting a pattern of a small area 100a in a row in the y-axis direction onto the sensitive substrate 110 with a pair of projection lenses as it is corresponds to each small area 100a. Sensitive substrate 1
The boundary region 1 is located between each of the ten transfer regions 110b.
A gap corresponding to 00b is generated. As a countermeasure, the pattern transfer position is corrected by deflecting the charged particle beam EB passing through each small area 100a in the y-axis direction by an amount corresponding to the width Ly of the boundary area 100b.

Also in the x-axis direction, the scattering transmission mask 100 and the sensitive substrate 11 are moved at a constant speed corresponding to the pattern reduction ratio.
In addition to moving 0, when the transfer of the small area 100a in one row is completed and transfer to the transfer of the small area 100a in the next row is performed, the charged particle beam EB is shifted by x by the width Lx of the boundary area 100b.
The pattern transfer position is corrected so that deflection in the axial direction does not cause a gap in the x-axis direction between the transfer target regions 110b.

As described above, in the division transfer method, a pattern corresponding to one die (one chip) on the mask 100 is divided into a number of small areas 110a, and a boundary area formed between the small areas 110a is formed. Since the lattice-shaped pillars are provided on 110b, the deflection and thermal distortion of the mask substrate due to the irradiation of the charged particle beam can be suppressed, and accurate exposure transfer can be performed.

A problem in achieving high throughput in the split transfer method is the proximity effect caused by reflected electrons from the wafer substrate. FIG. 3 shows the proximity effect and its cause. 3A shows an ideal stored energy distribution, FIG. 3C shows an actual stored energy distribution, and FIG. 3B shows the movement of electrons near the wafer surface. In FIG. 3, 1 indicates incident electrons, 2 indicates resist, 3 indicates a wafer, and 4 indicates reflected electrons.

The proximity effect means that if there are no reflected electrons, the proximity effect shown in FIG.
The resist having the stored energy distribution as shown in FIG. 3A actually has the stored energy distribution as shown in FIG. 3C, and a desired pattern is not formed during resist development. Refers to the effect. The cause is that the incident electrons 1 are reflected by the interaction with the atoms in the wafer 3 and diffused as shown in FIG.

As a method for correcting the proximity effect, a ghost method as shown in FIG. 4 has been proposed. When the energy accumulation distribution on the surface to be exposed is as shown in FIG. 4A, an exposure (ghost exposure) that produces the energy accumulation distribution as shown in FIG. 4B is added. (c)
This is a method of making a flat distribution as shown in FIG. The distribution in FIG. 4B is actually obtained by appropriately blurring the black-and-white inversion mask pattern of the mask that has been exposed to the pattern in FIG. However, in this method, since a process of exposing the reverse pattern after the exposure of the normal pattern is added, the substantial throughput of the electron beam exposure apparatus is reduced.

Therefore, GPWatson et al. (J. Vac. Sci. Technol.
B13 (6), p2504 to p2507, 1995) has proposed an exposure method as shown in FIG. In FIG. 5, 31 is a crossover position upstream of the mask, 32 is an electron beam passing through the center of the crossover, 33 is an illumination lens, 34 is a mask,
35 and 36 are transfer lenses, 37 is a wafer, 38 is a crossover position downstream of the mask, 39 is an aperture, 40
Is a hole close to a ring, 41 is an electron beam passing through the pattern portion of the mask 34, 42 and 43 are scattered electrons generated from portions other than the pattern of the mask 34, and 44 is an aperture 39.
Represents an electron beam cut by.

The electron beam 32 passing through the crossover position 31 is converted into a parallel beam by an illumination lens 33 and irradiates a mask 34. The electron beam 41 that has passed through the pattern portion of the mask 34 forms an image on the wafer 37 by the transfer lenses 35 and 36 and is transferred. At this time, a portion 44 of the beam is cut by an aperture 39 provided at a crossover position 38 downstream of the mask 34, and the opening angle of the image transfer system is determined by the size of the hole at the center of the aperture 39. Is done.

The aperture 39 has not only a hole at the center, but also an annular hole 40 around the hole. Electrons 4 scattered from portions other than the pattern of the mask 34
2 and 43 are imaged on the surface to be exposed by passing through the annular hole 40. However, since the opening angle determined by the annular hole 40 is very large, the image other than the pattern portion is blurred due to the spherical aberration of the transfer optical system. Therefore, according to this method, the image transfer of the pattern portion and the ghost exposure are performed at the same time, and the throughput of the exposure machine is not reduced.

[0018]

SUMMARY OF THE INVENTION GPWats as described above
The method such as on has the advantage of not lowering the throughput, but since the aperture angle for imaging the pattern on the mask 34 is determined by the aperture 39 in FIG. 5, it contributes to the exposure upstream of the aperture 39. There will be an electron beam 44 that does not exist. This electron beam 44
Does not contribute to imaging, but increases the blurring of the pattern on the exposed surface due to the so-called Coulomb effect. In addition, this type of aperture requires a beam position adjusting operation for aligning the center of the aperture 39 shown in FIG. 5 with the center of the beam crossover 38, and the accuracy thereof is required to be quite strict.

Further, the electron beam 44 irradiated on the aperture 39 increases unnecessary contamination on the aperture 39, drifts the beam due to charge-up of the contamination, and lowers beam position stability. Or the amount of current on the exposed surface of the mask 37 is changed.

The present invention has been made in order to solve such a problem, and it is possible to correct the proximity effect without lowering the throughput, and to reduce blur due to the Coulomb effect, and An object of the present invention is to provide an electron beam exposure apparatus in which a beam adjustment operation is easy and a beam position is stable.

[0021]

According to the present invention, there is provided a mask including a pattern portion through which most or all of the electrons pass and a portion other than a pattern in which the electrons are scattered, in the beam path of the electron beam optical column. An electron beam exposure apparatus configured such that a pattern is image-transferred onto a surface to be exposed by a lens system downstream of a mask, and forms an image on the surface to be exposed at a crossover position upstream of the mask. An aperture for determining the opening angle is provided, and an aperture for limiting the opening angle of the scattered beam from the mask is provided at a crossover position downstream of the mask, and is provided at a crossover position downstream of the mask. The size of the aperture is larger than the distribution diameter of the electrons transmitted through the mask pattern portion, and transmitted through the mask pattern portion. Proximity effect child occurs on the imaging plane, is solved by an electron beam exposure apparatus characterized by being sized to be corrected by the scattered electrons generated from the portion other than the mask pattern portion.

(Operation) According to the above means, the aperture for determining the opening angle when forming an image on the surface to be exposed is:
Since it is provided at the crossover position upstream of the mask, a useless electron beam that does not contribute to pattern image formation on the surface to be exposed can be cut before transmitting through the mask pattern portion. Therefore, the Coulomb effect and contamination caused by useless electron beams can be reduced.

The size of the aperture provided at the crossover position downstream of the mask is such that the proximity effect that electrons transmitted through the mask pattern generate on the image forming surface causes scattered electrons generated from portions other than the mask pattern portion. The ghost exposure for correcting the proximity effect can be simultaneously performed by the scattered electrons from portions other than the pattern portion of the mask. The actual size of the aperture is determined by performing a calibration test so that the proximity effect is corrected by scattered electrons generated from portions other than the mask pattern portion.

Further, since the size of the aperture provided at the crossover position downstream of the mask is larger than the distribution diameter of the electrons transmitted through the mask pattern portion, the alignment accuracy with respect to the aperture is not required. Time can be reduced.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, reference numeral 11 denotes an electron beam passing through the center of the crossover, reference numerals 12 and 13 denote illumination lenses, reference numeral 14 denotes a mask, reference numerals 15 and 16 denote transfer lenses, reference numeral 17 denotes a wafer, and reference numeral 18 denotes an aperture for limiting the size of an opening angle.
9 is a crossover position upstream of the mask 14, 20 is a crossover position downstream of the mask 14, and 21 is a mask 1
Aperture limiting aperture angle of scattered electrons from 4, 22
Denotes an electron beam transmitted through the pattern of the mask 14, 23,
Numeral 24 denotes scattered electrons generated from portions other than the pattern of the mask 14.

The electron beam 11 is applied to illumination lenses 12 and 13
The beam is converted into a parallel beam to irradiate the mask 14. The electron beam 22 transmitted through the pattern portion of the mask 14 is imaged and transferred onto the wafer 17 by the transfer lenses 15 and 16. An aperture 18 is provided at a crossover position 19 upstream of the mask 14, and the end of the crossover 19 is cut off by the aperture 18. If the shape of the crossover is Gaussian and the diameter of the aperture 18 is a diameter (FWHM) corresponding to half the height of the crossover, the aperture 18 cuts a half of the beam current. The aperture angle when forming the image of the mask 14 on the surface of the wafer 17 is determined by the aperture 18.

The crossover 19 is conjugated with the crossover 19 by the illumination lens 13 and the transfer lens 15.
Is imaged. The crossover 20 has a Gaussian shape with a cut end, and its size is smaller than the hole diameter of the aperture 21 provided at the position of the crossover 20. Electron beam 22 transmitted through the pattern portion of mask 14
Passes through the transfer lens 15 and forms an image on the wafer 17 with an opening angle determined by the size of the crossover 20. That is, the electron beam transmitted through the pattern portion of the mask 14 passes without being hindered by the aperture 21, and the entire amount contributes to imaging. Therefore, problems such as an increase in the Coulomb effect due to an extra electron beam and a problem that the beam position is temporally unstable due to accumulation of contamination in the aperture 21 do not occur.

The scattered electrons 23 and 24 generated from portions other than the pattern of the mask 14 pass through the transfer lens 15, are cut at the end by the aperture 21, and are bound on the wafer 17 with an opening angle determined by the size of the aperture 21. Image. The image of the scattered electrons has an opening angle determined by the size of the aperture 21 and the electron beam 22 transmitted through the pattern portion of the mask 14.
Is several times the aperture angle of the transfer lens 15, an image with blurring of several to several tens of μm is caused by aberrations such as spherical aberration of the transfer lenses 15 and 16, and the stored energy distribution in the resist on the wafer 17 is flattened. That is, the proximity effect due to the electron beam 22 transmitted through the pattern portion of the mask 14 is corrected without lowering the throughput.

[0029]

As described above, according to the present invention, in the beam path of the electron beam optical column, a mask including a pattern portion through which most or all of the electrons pass and a portion other than the pattern in which the electrons are scattered is arranged. An electron beam exposure apparatus configured such that a mask pattern is image-transferred onto a surface to be exposed by a lens system downstream of the mask, and forms an image on the surface to be exposed at a crossover position upstream of the mask. An aperture for determining the opening angle at the time of performing is provided, and at a crossover position downstream of the mask,
An aperture for limiting the opening angle of the scattered beam from the mask is provided, and the size of the aperture provided at the crossover position downstream of the mask is larger than the distribution diameter of the electrons transmitted through the mask pattern portion, and An electron beam exposure apparatus, wherein the proximity effect in which the transmitted electrons are generated on the image forming surface is sized to be corrected by scattered electrons generated from a portion other than the mask pattern portion. Does not lower the throughput.

Further, since unnecessary electron beams are cut before passing through the mask pattern portion, blurring due to the Coulomb effect can be reduced, and a sharper image can be expected as compared with conventional optical systems. .

Further, since the aperture provided at the crossover position downstream of the mask has a sufficiently large hole diameter, the beam position can be easily adjusted, and the accumulation of contamination is reduced, so that the beam position can be temporally changed. Stabilize.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing an outline of a division transfer method.

FIG. 3 is a diagram showing a proximity effect and its cause.

FIG. 4 is a diagram illustrating the principle of a ghost exposure method.

FIG. 5 is a diagram showing an outline of an exposure method proposed by GPWatson et al.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Incident electron 2 Resist 3 Wafer 4 Backscattered electron 11 Electron beam passing through the center of crossover 12, 13 Illumination lens 14 Mask 15, 16 Transfer lens 17 Wafer 18 Aperture for limiting the size of opening angle 19 Crossover position upstream of mask Reference Signs List 20 Crossover position downstream of mask 21 Aperture limiting aperture angle of scattered electrons from mask 22 Electron beam transmitted through mask pattern 23, 24 Scattered electrons 31 Crossover position upstream of mask 32 Electrons passing through center of crossover Beam 33 Illumination lens 34 Mask 35, 36 Transfer lens 37 Wafer 38 Crossover position downstream of the mask 39 Aperture 40 Hole near the ring 41 Electron beam 42, 43 which has passed through the pattern part of the mask Electron beam 30 crossover point 100 mask 100a small area on mask 100b boundary area on mask 110 sensitive substrate 110a area for one die of sensitive substrate 110b transferred area of sensitive substrate corresponding to small area 100a AX charged particle beam Optical axis of optical system EB charged particle beam CO Crossover point of optical system

Claims (1)

[Claims] 1. A mask comprising a pattern portion through which most or all of electrons are transmitted and a portion other than a pattern in which electrons are scattered is disposed in a beam path of an electron beam optical column, and the mask pattern is a lens system downstream of the mask. An electron beam exposure apparatus configured to be image-transferred onto a surface to be exposed by the method described above, wherein at a crossover position upstream of the mask, an opening angle at the time of forming an image on the surface to be exposed is determined. The aperture is provided at the crossover position downstream of the mask, an aperture for limiting the opening angle of the scattered beam from the mask is provided, and the size of the aperture provided at the crossover position downstream of the mask is The proximity of the distribution diameter of the electrons transmitted through the mask pattern portion and larger than the distribution diameter of the electrons transmitted through the mask pattern portion on the image forming surface. An electron beam exposure apparatus characterized in that the size is such that the effect is corrected by scattered electrons generated from portions other than the mask pattern portion.