JPH07135144A - Charged particle beam aligner - Google Patents

Abstract

PURPOSE:To provide a charged particle beam aligner capable of exposure with higher efficiency as compared with the prior art, while restraining the defocusing of charged particle beam caused by the space charge effect. CONSTITUTION:In an aligner wherein specified regions of a mask 5 are simultaneously irradiated with electron beam B from an electron gun 1, and patterns formed on the specified regions are transferred to a photosensitive substrate W via projection lenses 6, 7, the focal lengths of the projection lenses 6, 7 are made short by decreasing positive voltages supplied to cylinders 62, 72 inserted into the projection lenses 6, 7, as the packing of patterns in the specified regions on the mask 5 is large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for transferring a pattern formed on a mask by a charged particle beam onto a photosensitive substrate such as a semiconductor wafer.

[0002]

2. Description of the Related Art Conventionally, in this type of apparatus, when the beam current of a charged particle beam with which a mask is irradiated is large, the beam is blurred due to the space charge effect, and it is difficult to correctly transfer the mask pattern onto the photosensitive substrate. Become. For this reason, the exposure is performed with the beam current reduced to such an extent that the effect of the space charge effect can be ignored.

[0003]

However, if the beam current is small, it takes a long time for exposure and the throughput is lowered. In addition, since the same region is exposed for a long time, the resist on the photosensitive substrate is heated to cause thermal expansion, which lowers the exposure accuracy.

By the way, the generally recognized space charge effects of charged particle beams are classified into the following three types. As a result of the charged particle beams colliding with each other and exchanging their energies, the energy width of the charged particle beams widens. The effect that the orbits of the charged particle beams are bent when they collide with each other. Due to the space charge of the charged particle beam, the beam of the charged particle beam spreads as a whole, resulting in the focal position of the charged particle beam moving far.

Tran for a projection lens that focuses a charged particle beam
As long as the sverse chromatic aberration (visual field chromatic aberration) is sufficiently corrected, the beam blur due to the effect of is small and can usually be ignored. Further, in the vicinity of the crossover where the charged particle beams are concentrated, the above-mentioned space charge effect becomes relatively large. However, such a region is only about 1/100 to 1/10 of the total optical path length of the charged particle beam, and the space charge effect due to this effect does not pose a problem. Regarding the space charge effect of, the total beam current passing through the pattern of the mask, no matter how far apart the charged particle beams are, which are passing through the pattern (corresponding to the beam transmitting portion) formed in the mask and toward the photosensitive substrate. Blurring occurs in proportion to. In particular, in an exposure apparatus that irradiates a relatively large area on the mask at one time and transfers the patterns within that area to the photosensitive substrate at once, the beam current when viewed over the entire irradiation area is
Since it is considerably larger than a drawing type exposure apparatus that draws patterns one by one, a large blur occurs on the photosensitive substrate. In order to avoid this blur, in the conventional apparatus, the beam current itself for irradiating the mask had to be set to a very small value.

An object of the present invention is to provide a charged particle beam exposure apparatus capable of performing exposure more efficiently than before while suppressing blurring of the charged particle beam due to the space charge effect.

[0007]

1 and 2, which show an embodiment, the present invention is directed to irradiating a specific area SF of a mask 5 with a charged particle beam B at the same time to obtain the specific area SF. It is applied to a charged particle beam exposure apparatus that transfers the pattern 5a formed on the photosensitive substrate W via the projection lenses 6 and 7. Then, the larger the filling rate of the pattern 5a in the specific range SF on the mask 5, the shorter the focal lengths of the projection lenses 6 and 7 are.
The above-mentioned object is achieved by providing the focus control means 10, 62, 72 for controlling the optical axis 7. Pattern 5a here
The filling rate is a value obtained by dividing the area of the pattern 5a formed in the specific range SF of the mask 5 by the area of the specific range SF. In the apparatus of claim 2, the focus control means changes the focal length of the projection lenses 6 and 7 by adjusting the voltage applied to the metal cylinders 62 and 72 inserted in the projection lenses 6 and 7.

[0008]

The beam current of the charged particle beam B with which the specific area SF on the mask 5 is irradiated by one exposure is changed to the specific area S.
If it is constant regardless of the area of F, the beam current of the charged particle beam B passing through the pattern 5a in the specific range SF changes according to the filling rate of the pattern 5a in the specific range SF, and the beam current increases as the filling rate increases. Will increase. Therefore, the greater the pattern filling rate, the greater the space charge effect of the charged particle beam B that has passed through the mask 5,
The focus position is going to move away. Here, in the present invention, since the projection lenses 6 and 7 are controlled so that the larger the filling rate of the pattern 5a is, the shorter the focal lengths of the projection lenses 6 and 7 are. The change in the focal length of No. 7 is offset and the blur of the charged particle beam B on the photosensitive substrate W is suppressed.

In the apparatus of claim 2, when the applied voltage to the metal cylinders 62 and 72 inserted in the projection lenses 6 and 7 is increased or decreased, the passing speed of the charged particle beam B in the projection lenses 6 and 7 changes. Then, the refraction of the charged particle beam B by the projection lenses 6 and 7 changes. As a result, the focal lengths of the projection lenses 6 and 7 change.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an outline of an exposure apparatus of this embodiment, and 1 is an electron gun as a source of a charged particle beam. The electron beam B emitted from the electron gun 1 is deflected by the condenser lens 2 and forms an image on the crossover C1 at the center of the deflector 3. The electron beam B passing through the crossover C1 is deflected in a predetermined direction by the deflector 3,
Mask 5 after being corrected to a parallel beam by condenser lens 4
Reach a certain range of.

As shown in FIG. 2, the mask 5 has a transparent portion 5a (hatched area in the drawing) for transmitting an electron beam. The mask 5 is divided into a plurality of sub-fields of view SF, one of which is the deflector 3 shown in FIG.
The electron beam B that has passed through is irradiated. The sub-field of view S
The area of F and the shape of the transmission part 5a are not constant, and in the illustrated example, the right sub-field SF has a larger area than the left sub-field SF. The total area of the transmissive portion 5a is larger in the left sub-field of view SF.

As shown in FIG. 1, the electron beam B which has passed through the transmission part 5a of any one of the sub-fields SF of the mask 5.
Is condensed by the first projection lens 6 and crossed over C
Image to 2. The electron beam B that has passed through the crossover C2 is transmitted by the second projection lens 7 to the optical axis A of the electron gun 1.
The beam is corrected into a beam parallel to and reaches a specific position on the wafer W. As a result, the shape of the transmission part 5a formed in the sub-field of view SF of the mask 5 is transferred onto the resist of the wafer W at a magnification corresponding to the refractive index of the lenses 6 and 7. Projection lens 6,
Reference numeral 7 covers coils 60 and 70 for generating a magnetic field according to a current supplied from a power source (not shown) with ferromagnetic bodies 61 and 71, and a non-magnetic body such as a copper cylinder 62 on the inner peripheral side of the coils 60 and 70. , 72 are inserted. The cylinders 62 and 72 are supported in an insulating state in a vacuum container (not shown) through which the electron beam B passes.

In the cylinders 62 and 72 of the projection lenses 6 and 7,
A voltage on the positive electrode side is applied from the CPU 10 via the interface 11 and the voltage amplifier 12, and the focal lengths of the projection lenses 6 and 7 change according to the applied voltage. That is, as the voltage applied to the cylinders 62 and 72 increases,
The velocity of the electron beam B passing through the cylinders 62, 72 increases, and the focal lengths of the projection lenses 6, 7 become longer.

The CPU 10 has a microcomputer and its peripherals, controls the operation sequence of each part of the exposure apparatus in accordance with an exposure program written in a memory (not shown), and sets the sub-field of view SF designated on the exposure program. The voltage applied to the deflector 3 is controlled so that the electron beam B reaches and the deflection direction and the deflection amount of the electron beam B are adjusted. Further, the CPU 10 controls the voltage applied to the cylinders 62 and 67 according to the designated sub-field of view SF.

In the memory of the CPU 10, a first data table indicating the voltage to be applied to the deflector 3 for each sub-field of view SF of the mask 5, and the voltage to be applied to the cylinders 62 and 72 for each sub-field of view SF are indicated. And a second data table. In the second data table, the larger the filling rate of the pattern in the sub-field of view SF (total area of transmissive portions 5a in sub-field of view SF / area of sub-field of view SF), the larger the cylinder 6 is.
The voltage applied to 2, 72 becomes smaller. In the example of FIG. 2, since the pattern filling rate of the right sub-field of view SF is smaller than that of the left sub-field of view SF, the voltage applied to the cylinders 62 and 72 corresponding to the right sub-field of view SF is on the left side. Sub-field of view SF
Is specified to be larger than the applied voltage to the cylinders 62 and 72 corresponding to.

FIG. 3 shows various types of processing executed by the CPU 10, particularly the deflector 3 and the cylinder 6 of the projection lenses 6 and 7.
It is a flow chart which shows the processing procedure concerning adjustment of the applied voltage to 2,72. When a specific sub-field of view SF of the mask 5 is designated as an irradiation target by an electron beam by an exposure program that instructs the operation of the entire exposure apparatus, the processing by the illustrated program is started. First, in step S1, the sub-field of view SF designated by the exposure program is recognized. In the next step S2, the voltage applied to the deflector 3 corresponding to the designated sub-field of view SF is determined by the above-mentioned first data table, and the result is stored. Continuing step S3
Then, the applied voltage to the cylinders 62 and 72 corresponding to the designated sub-field of view SF is determined by the second data table described above, and the result is stored. Then, in step S4, a signal corresponding to the applied voltage determined in steps S2 and S3 is output in parallel to the interface 11, and the voltage amplifier 12
Is converted into a predetermined voltage by the deflector 3 and the cylinders 62 and 72.
Apply to. After the processing of step S4, the process returns to the exposure program that controls the overall exposure operation, and the designated sub-field of view S
Start exposure to F.

According to the above processing, each time the specific sub-field of view SF of the mask 5 is designated as the exposure target, the cylinders 62, 72 are formed according to the second data table created in advance.
The voltage applied to the projection lenses 6 and 7 is adjusted to change the focal length. In the second data table, as described above, the larger the pattern filling rate is, the smaller the voltage applied to the cylinders 62 and 72 is specified. In the sub-field of view SF having a relatively short focal length and a small filling rate, the focal lengths of the projection lenses 6 and 7 are relatively long.

On the other hand, since the beam current of the electron beam emitted from the electron gun 1 to the sub-field of view SF is constant, the mask 5
The beam current of the electron beam passing through the transparent portion 5a increases as the pattern filling rate increases, and the focus of the electron beam moves far due to the space charge effect described above. The movement of the focus due to this space charge effect is caused by the above-mentioned projection lens 6,
Offset by a change in focal length of 7, resulting in
The blurring of the electron beam on the wafer W is suppressed. If the applied voltage to the cylinders 62 and 72 designated on the second data table is precisely determined by experiment or computer simulation, it is possible to completely prevent the electron beam from being blurred regardless of the type of the sub-field of view SF. Is. Therefore, the beam current of the electron beam B emitted from the electron gun 1 can be increased more than in the conventional case, the exposure time of the sub-field of view SF can be shortened, and the throughput can be greatly improved. Note that in a normal exposure apparatus, various setups are performed prior to the exposure for each sub-field of view SF, so if the processing of FIG.
Even if the focal length is adjusted for each sub-field of view SF, the time required for setup before exposure does not change.

Further, in the embodiment, the voltage applied to the cylinders 62 and 72 inserted in the projection lenses 6 and 7 is adjusted to electrostatically increase or decrease the focal length of the projection lenses 6 and 7. The focal lengths of the projection lenses 6 and 7 can be adjusted in a much shorter time than in the case where focus adjustment is performed by changing the current supplied to the coils 60 and 70 of 7. That is, when the magnetic field itself is adjusted by changing the current supplied to the coils 60 and 70, the ferromagnetic material 6 surrounding the coils 60 and 70 is used.
It is not possible to change the magnetic field faster than the response speeds of 1 and 71, and it takes a considerable time for the focal points of the projection lenses 6 and 7 to settle at positions corresponding to changes in the coil current. On the other hand, in the embodiment, only the voltage applied to the cylinders 62 and 72 is changed, so that the focal points of the projection lenses 6 and 7 move quickly to the target position. Further, since the coils 60 and 70 are installed outside the vacuum container that allows the electron beam to pass therethrough, the coil 6
An eddy current flows through the wall of the metal vacuum container in the process in which the magnetic field of 0, 70 acts in the vacuum region where the electron beam passes, and this also increases the settling time, but the cylinder 62,
Since 72 can be placed in a vacuum vessel, such waiting time does not occur.

In the embodiment, a second data table that specifies the focal lengths of the projection lenses 6 and 7 for each sub-field of view SF is created, and the focus adjustment is performed by referring to the second data table each time the sub-field of view SF is specified. However, the present invention is not limited to such an aspect, and for example, the filling rate of the pattern may be calculated from the design data of the sub-field of view SF, and the focal length may be obtained corresponding to the calculation result.

In the correspondence between the above embodiment and the claims,
The sub-field of view SF of the mask 5 covers a specific range of the mask
The transparent portion 5a constitutes a mask pattern, the wafer W constitutes a photosensitive substrate, and the CPU 10 and the cylinders 62 and 72 constitute focus control means.

[0023]

As described above, according to the present invention, the change in the focal position due to the space charge effect of the charged particle beam passing through the mask pattern and the change in the focal length of the projection lens are canceled out. The exposure time can be shortened by increasing the beam current of the charged particle beam with which the mask is irradiated while suppressing the blurring of the charged particle beam on the photosensitive substrate due to the space charge effect, and the throughput can be greatly improved. By shortening the exposure time, the thermal expansion of the resist is suppressed and the exposure accuracy is greatly improved. In the apparatus of the second aspect, it is possible to shorten the settling time when changing the focal length of the projection lens and further improve the throughput.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an exposure apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged view showing a part of the mask shown in FIG.

FIG. 3 is a flowchart showing a focus control procedure in the CPU of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron gun 5 Mask 5a Transmission part of mask 6,7 Projection lens 10 CPU 60,70 Coil 62,72 of projection lens Cylindrical B electron beam SF inserted in the projection lens Subfield of view W mask Wafer

Claims (2)

[Claims] 1. A charged particle beam exposure apparatus which simultaneously irradiates a specific area of a mask with a charged particle beam and transfers a pattern formed in the specific area onto a photosensitive substrate through a projection lens. A charged particle beam exposure apparatus comprising: focus control means for controlling the projection lens such that the greater the filling rate of the pattern in the range is, the shorter the focal length of the projection lens is. 2. The charged particle beam exposure apparatus according to claim 1, wherein the focus control unit changes the focal length by adjusting a voltage applied to a non-magnetic cylinder inserted in the projection lens. A charged particle beam exposure apparatus characterized by the above.