JPH10223514A - Electron beam transferring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron beam transferring apparatus having a high- emittance low-brightness optical source and high throughput with a uniform irradiation intensity of a reticle. SOLUTION: This electron beam transferring apparatus comprises an electron gun 3 for emitting an electron beam, condenser lenses 9, 15 which adjusts the electron beam with an aperture 19, a reticle 23 for shaping the irradiated beam and projection lens systems 27, 31 for forming an image of the shaped beam on a sample surface 33 to form a pattern thereon. It operates the electron gun 3 within a temp.-limited range and forms the image of a crossover 7 formed by the electron beam 3 on the surface of the reticle 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer apparatus for transferring a reticle (mask) pattern onto a sample (eg, a wafer) using an electron beam. In particular, the present invention relates to a transfer device using an electron beam that can form a high-density and fine pattern of 4G DRAM or later with high throughput.

[0002]

2. Description of the Related Art As one type of lithography apparatus for printing an integrated circuit pattern on a semiconductor wafer, a mask provided with a predetermined pattern is irradiated with an electron beam, and the image of the pattern in the irradiation range is reduced to a wafer by a two-stage projection lens. 2. Related Art An electron beam reduction transfer device for transferring is known (for example, refer to Japanese Patent Application Laid-Open No. 5-160012). In this type of apparatus, since the entire area of the mask cannot be irradiated with the electron beam at a time, the field of view of the optical system is divided into a number of small areas, and the pattern image is transferred by dividing each small area ( For example, US Pat.
No. 60151).

In this type of conventional electron beam transfer apparatus, the electron gun is generally operated in a space charge limited region. Here, the space charge limiting region means that the cathode temperature is relatively low and the current density of the electron beam emitted from the electron gun is sensitively affected by the applied voltage (acceleration voltage) between the anode and the cathode. It is the area that is not affected much. In addition, as a reticle illumination system, a Koehler illumination system or a critical Koehler illumination system has been used.
Here, the Koehler illumination system is a system in which a reticle surface is illuminated with a beam diverging from a light source and a crossover image created by an electron gun is formed on an entrance pupil of an objective lens. Do). The critical Koehler illumination system is a system in which an image of a cathode of an electron gun is formed on a reticle surface, and a crossover image formed by the electron gun is formed on an entrance pupil of an objective lens.

[0004]

The electron gun operating in the space charge-limited region described above has a small luminance and it is difficult to increase the emittance. Therefore, the electron beam of the split transfer system (US Pat. No. 5,260,151) is used. There is a problem that it is difficult to use the transfer device. In the case of the Koehler illumination system and the critical Koehler illumination system, the non-uniformity of the electron emission on the cathode surface appears directly as the non-uniformity of the reticle illumination. There is a problem that it is difficult to obtain uniform reticle illumination intensity.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and has an object to provide a high throughput electron source having a high emittance and low luminance light source and a uniform reticle irradiation intensity. It is an object to provide a line transfer device.

[0006]

In order to solve the above-mentioned problems, an electron beam transfer apparatus according to the present invention adjusts an electron beam emitted from an electron gun with a condenser lens and an opening, irradiates a reticle, and irradiates the reticle with the reticle. An electron beam transfer apparatus for forming a pattern on a sample surface by imaging a shaped electron beam on a sample surface with a projection lens system; and forming an image of a crossover formed by the electron gun on a reticle surface. It is characterized by.

In order to operate the electron gun in a temperature-limited region,
By using an appropriately sized cathode (for example, a diameter of 2 mm or more), the electron gun can have a high emittance (for example, 1, 2).
000 μm · mrad or more), low brightness (for example, 10 ³ A /
cm ² · sr or less). On the other hand, assuming that the operating condition of the cathode of the electron gun is a temperature limiting region, an electron beam having a high current density is emitted from a region having a low work function on the cathode surface, and an electron beam having a low current density is emitted from a region having a high work function. In this case, the brightness can be changed depending on the direction in which the electron beam diverges from the crossover, and the current density for irradiating the reticle is not uniform under the Koehler illumination condition or the critical Koehler illumination condition (details will be described later with reference to FIG. 2). Dose is not uniform. However, in the present invention, instead of illuminating the reticle with the electron beam diverging from the crossover, an enlarged image of the crossover is created, and the reticle is illuminated with this enlarged image. Therefore, in the crossover, since the electron beam has a Gaussian intensity distribution, the reticle is illuminated with the electron beam near the center thereof, and the illumination intensity of the reticle becomes uniform.

In the embodiment described later, a change in luminance due to a diverging direction from the crossover causes a change in intensity on an aperture provided between two projection lenses. Since it is designed to be sufficiently smaller than the aperture diameter, the intensity change does not give an intensity change to each small area of the visual field.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an electron beam transfer apparatus according to the present invention, at least two stages of the condenser lens are arranged,
It is preferable to make the magnification of the crossover variable and thereby make the aperture angle of the electron beam imaged on the sample surface variable.
If there are at least two condenser lenses between the electron gun and the reticle, the size of the crossover image or the angle of divergence from the reticle can be changed without changing the crossover imaging condition on the reticle. The aperture angle can be arbitrarily changed (with a margin in emittance). Therefore, since the aperture angle can be varied only by changing the lens condition, there is an advantage that the aperture can be easily adjusted to the optimal aperture, and the current density and the beam resolution can be varied.

In the present invention, the cathode of the electron gun may be made of LaB ₆ or an oxide cathode material. Since the work function may have location dependence on the cathode surface, LaB ₆ , barium oxide, or an impregnated type cathode (such as BaO impregnated in the W skeleton) can be used.
Since these cathodes can be used at a low operating temperature, a beam having a small energy width (a small energy dispersion) can be formed.

A description will be given below with reference to the drawings. FIG.
1 is an image diagram of an optical system of an electron beam transfer device according to one embodiment of the present invention. An electron gun 3 is arranged at the top of the optical system 1 of the electron beam transfer device. This electron gun 3 has a single crystal La
The cathode 5 made of B ₆ (diameter approximately 2 mm) having a. A heater (not shown) is provided around the cathode 5 to heat the cathode 5. The operating temperature of the cathode 5 is about 1,150 ° C. in a temperature limited region, and the brightness is made variable by changing the temperature.

FIG. 2 is a diagram showing an image formation state immediately below the electron gun cathode in the electron beam transfer apparatus optical system of FIG. Each point 5a, 5a on the electron emission surface (lower end surface) of the electron gun cathode 5
The electron beams emitted from b and 5c form a crossover 7 immediately below the cathode 5. The electron beam diverges from the crossover 7 with a spread of about ± 10 mrad downward.

FIG. 3 is a graph showing the distribution of electron beam current density in the direction perpendicular to the optical axis at the crossover just below the electron gun in FIG. In the crossover 7, the current density is a value obtained by integrating the electron beam emission from each part 5a, 5b, 5c of the cathode 5, and the radius dependence of the current density draws a Gaussian distribution curve. In the critical lighting system of the present invention,
The reticle 6 is illuminated by extracting and enlarging a portion (oblique line in the figure) showing a substantially uniform distribution at the center of the curve, and forming an image on the surface of the reticle 6. In the crossover 7 part, each part 5a, 5b, 5
c, the electron beam emission from the reticle 6 is averaged.
Does not become non-uniform.

On the other hand, each point 5a, 5b, 5c of the cathode 5
After the electron beam emitted from the
An image is formed at points 41a, 41b and 41c, respectively, and an image 41 of the cathode 5 is formed below the crossover 7. In the cathode image 41, the non-uniformity of the electron beam emission amount at each point of the cathode is carried over as it is. Therefore, in the Koehler illumination system in which the cathode image 41 is formed on the reticle 6 and illuminated, the non-uniformity is carried over as it is, and the illumination intensity cannot be uniform. However, in the critical illumination system of the present invention, as described above, the illumination intensity of the reticle 6 is uniform even when the electron beam emission distribution of the cathode 5 is not uniform.

The description will be continued with reference to FIG. Electron gun 3
Are arranged below, two-stage condenser lenses 9 and 15 are arranged.
Is imaged. A beam limiting aperture 11 is provided at the same level as the first-stage condenser lens 9. This beam limiting aperture is for removing a beam emitted in a direction of a large angle with respect to the optical axis direction. The magnification of the image by the two-stage condenser lenses 9 and 15 can be calculated by using the dimensions A, B, C and D between the lenses 9 and 15 and the image points 7, 13, and 17 in the figure. (B / A) × (D
/ C). This magnification is determined by the first condenser lens 9.
Is changed by changing the position of the imaging point 13 up and down. That is, the two-stage condenser lenses 9 and 1
Reference numeral 5 serves as a zoom lens.

The rectangular opening 19 adjusts the outer shape of the enlarged image of the crossover image and passes only the portion where the intensity at the central portion is flat to the bottom. This enlarged image is formed again on the reticle 23 by the condenser lens 21 to illuminate a predetermined portion of the reticle 23. The electron beam patterned through the reticle 23 is reduced by the two-stage projection lenses 27 and 31 and is imaged on the surface of the sample (wafer) 33. An appropriate resist is applied to the surface of the wafer 33,
A pattern corresponding to the electron beam dose is formed on the surface of the wafer 33.

A crossover opening 29 is provided at a position where the space between the reticle 23 and the wafer 33 is internally divided at a reduction ratio. The aperture 29 determines the aperture value or adjusts the beam so that the principal ray intersects the optical axis at this aperture position. FIG. 4 is a graph showing an electron beam intensity distribution at a crossover opening of the optical system of the electron beam transfer apparatus of FIG. As shown in FIG. 4, the beam intensity distribution in the crossover aperture 29 is non-uniform in electron beam emission at the cathode 5 (non-uniformity of electron beam emission angle-luminance distribution from the crossover 7). Is reproduced. But,
If the diameter of the crossover opening 29 is sufficiently larger than the width of the beam intensity distribution at this position, there is no problem even if the beam intensity distribution is not uniform at this position.

When the intensity of the electron beam emitted from the crossover of the electron gun is dispersed in a very wide range, the distribution of the intensity of the electron beam at the crossover aperture 29 is as shown by a dotted line 41 in FIG. In this case, the aperture 11 may be provided on the first or second condenser lens 9 or 15.

In this embodiment, since the cathode operates under the temperature limiting condition, the brightness of the electron beam can be easily adjusted to an arbitrary value by changing the temperature of the cathode. If a cathode having a large diameter (for example, 2 mm or more) is used, emittance can be increased. In addition, even if the angular distribution of the luminance varies minutely due to the variation in the work function of the cathode surface, the reticle illumination can be made uniform, so that high-accuracy transfer is possible.

[0020]

As apparent from the above description, according to the present invention, there is provided a high-throughput electron beam transfer apparatus having a high emittance and low luminance light source and having a uniform reticle irradiation intensity. be able to.

[Brief description of the drawings]

FIG. 1 is an imaging diagram of an optical system of an electron beam transfer device according to one embodiment of the present invention.

FIG. 2 is a diagram showing an image forming state immediately below an electron gun cathode in the electron beam transfer device optical system of FIG. 1;

3 is a graph showing a distribution of electron beam current density in a direction perpendicular to an optical axis in a crossover immediately below an electron gun in FIG. 2;

4 is a graph showing an electron beam intensity distribution at a crossover aperture between projection lenses of the electron beam transfer device optical system of FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 electron beam transfer device optical system 3 electron gun 5 cathode 7 crossover 9, 15 condenser lens 11 beam limiting aperture 13, 17, 25, 35 imaging point 19 rectangular aperture 21 condenser lens 23 reticle 27 first projection lens 29 crossover Aperture 31 Second projection lens 33 Wafer 41 Cathode image

Claims (3)

[Claims] An electron beam emitted from an electron gun is adjusted by a condenser lens and an opening, and is irradiated with a reticle. An electron beam shaped by the reticle is imaged on a sample surface by a projection lens system to form an image on the sample surface. An electron beam transfer device for forming a pattern on a reticle surface, the image being formed by the electron gun. 2. The method according to claim 1, wherein the condenser lens is arranged in at least two stages to make the magnification of the crossover variable, thereby changing the aperture angle of the electron beam imaged on the sample surface. An electron beam transfer device as described in the above. 3. The electron beam transfer apparatus according to claim 1, wherein the cathode of said electron gun is made of LaB ₆ or an oxide cathode material.