JP2000243334A - Electron gun and control method for electron gun - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the homogeneity of electron beam intensity by independently controlling the voltages of a plurality of heaters for applying electron impacts to the back face of a cathode having an electron emission face. SOLUTION: Eight heaters 5, for example, are radially provided at uniform intervals below a back face corresponding to a ring-like electron emission face 6 of a cathode 3, and a DC heating power supply 7 and a bombard voltage 8 are connected to the heaters 5. Electro-bombards from the heaters 5 hit the back face, and the generated heat heats the electron emission face 6. The electron intensity distribution displayed on a CRT is observed, heaters 5 requiring voltage control are specified among a plurality of heaters 5, bombard voltage values are checked for the optimum intensity distribution, and the heaters 5 are independently controlled via an interface 9 by the instruction from a CPU connected to the interface 9. The number of the heaters 5 is optionally determined according to the size of the cathode 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron gun having electron beam (beam) intensity distribution uniformity suitable for an electron gun for an electron beam reduction transfer apparatus.

[0002]

2. Description of the Related Art In a conventional transfer apparatus of this type, an electron gun having an axially symmetric structure having three electrodes of a cathode, a Wehnelt, and an anode used in a temperature-limited region has been used. Here, the cathode and the Wehnelt are insulated from each other and have a structure in which different potentials (potentials) are applied.

It is known to form a hollow beam in order to reduce the influence of the space charge effect when projecting a mask image onto a wafer.

[0004]

However, as shown in FIG. 3, in the temperature-limited region, the current density greatly changes in response to a temperature change. If the temperature is uneven or the work function of the surface is uneven, the intensity distribution of the electron beam (beam) is not uniform, and the mask (reticle) cannot be uniformly illuminated. There is a problem that the dimensional accuracy of the formed pattern is deteriorated.

In particular, in the case of an electron gun used in a transfer system in which the transfer area per shot is increased (1 mm × 1 mm on a mask), which can correspond to the actual production of the next-generation DRAM, the cathode surface becomes large accordingly. Φ3-10m
m, this problem becomes significant. Therefore,
SUMMARY OF THE INVENTION An object of the present invention is to provide an electron gun suitable for an electron gun for an electron beam reduction transfer device and capable of obtaining uniformity of electron beam (beam) intensity distribution.

[0006]

SUMMARY OF THE INVENTION The present invention first provides a cathode having an electron emission surface, an anode for extracting electrons,
An electron gun provided with a heater for applying an electron impact to the back surface of the cathode, wherein the heater comprises a plurality of heaters that can be independently controlled in voltage.

The present invention also provides a second aspect of the invention wherein the plurality of heaters are arranged on the back surface of the cathode at substantially equal intervals radially from the center of the cathode. 2) ”. Further, the present invention has a third feature that "an electron beam (hollow beam) having a ring-shaped cross section is emitted from the electron emission surface.
Or 2) (claim 3).

Further, the present invention is directed to a fourth aspect, "a small hole provided in a plane including a nearby position where a cathode image or a crossover image is formed and sufficiently away from an optical axis; 4. The method for controlling an electron gun according to claim 1, wherein the method is used in an electron beam reduction transfer device including a detector provided below and a deflector provided above the small hole. The emitted electron beam is deflected by the deflector, scans over the small holes, detects the electrons passing through the small holes by the detector, and from the electron beam intensity distribution that is the detection result,
A method of controlling an electron gun (claim 4), wherein voltage control of the plurality of heaters is performed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electron gun according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a schematic sectional view of the electron gun of the embodiment, and FIG. 1B is a schematic bottom view. This electron gun includes an anode 1, a control anode 2, a cathode 3, a heater (sub-cathode) 5, and the like, which are coaxially arranged in a line.

In this embodiment, an electron gun without a Wehnelt is shown. However, the present invention can be applied to an electron gun with a Wehnelt. The anode 1 is in the form of a plate having a hole at the center, and usually has a ground level potential.
The anode 1 functions to extract an electron beam from the cathode 3 to which a negative voltage (acceleration voltage) is applied.

By optimizing the hole diameters and positions of the anode 1 and the control anode 2 by simulation, it is possible to obtain a high emittance condition while minimizing the aberration of the lens effect. The control anode 2 is also in the form of a plate having a hole at the center, and is disposed between the anode 1 and the cathode 3 in parallel with the anode 1.

The cathode 3 is made of tantalum, and on its surface, an iridium film or a rhenium film is formed except for a ring-shaped electron emission surface 6. More specifically, Φ1
3. 0 mm radius of the 0 mm cathode surface and 4.
An iridium film or a rhenium film was deposited in a range of 5 to 5 mm, and tantalum was exposed in a range of a radius of 4.5 to 5 mm so that electrons were emitted from the tantalum.

The work function of iridium is 5.3 eV, and the work functions of tantalum and rhenium are 4.1 eV, respectively.
Since it is 9 eV and 4.7 eV, iridium has a higher work function than tantalum and rhenium. Therefore, the cathode temperature can be determined such that the electron beam is emitted only from the electron emission surface made of ring-shaped tantalum.

Since the film material is conductive, the potential is basically the same as that of the electron emission surface 6 of the cathode 3, so that the electric field near the electron emission surface 6 is not disturbed. Eight heaters 5 are radially provided at equal intervals below the position of the back surface corresponding to the ring-shaped electron emission surface 6 of the cathode 3.
Each heater 5 is connected to a DC heating power supply 7 and a bombard voltage 8. The electron bombard from the heater 5 hits the rear surface. The heat generated thereby heats the electron emission surface 6. Also, each bombard voltage 8 is C
It can be independently controlled by a PU control interface 9.

In the example of this embodiment, eight heaters 5 are arranged radially below the back surface of the cathode at equal intervals. However, the number of heaters 5 is arbitrary according to the size of the cathode 3. Can be determined. The cathode 3 has a support member (ceramic) made of an insulating material at its center.
It is fixed by 10.

Next, a control method when the electron gun according to the embodiment is applied to an electron beam reduction transfer apparatus will be described with reference to FIG. FIG. 2 is a diagram schematically illustrating a configuration of an electron beam reduction transfer device using the electron gun according to the embodiment. The dashed line indicates which of the cathode surfaces is electro-optically conjugate.

The solid line shows where the flat portion emitted from the electron gun and formed near the crossover is electron-optically conjugate. The electron beam emitted from the electron gun 21 is focused by the first condenser lens 22, further focused by the second condenser lens 23, and formed at the inside of the second condenser lens 22. The electron beam thus formed is irradiated on a mask (reticle) 30 by an irradiation lens 29.

Of the electron beams applied to the mask 30, those passing through the openings (patterns to be transferred to the photosensitive substrate) formed in the mask 30 are the first projection lens 31 and the second projection lens 32. On the photosensitive substrate 33
Is irradiated. Thereby, the pattern is projected on the photosensitive substrate 33 and printed. In addition, in the electron beam reduction transfer device of the present embodiment, a first small hole (about 2 μm in diameter) is provided in the same plane as the molding opening 24 and sufficiently away from the optical axis.
m) 25 is formed, and a first detector (Faraday gauge) 26 for detecting an electron beam passing through the small hole 25 is provided below the small hole 25.

Also, a position which is within the same plane as the contrast aperture 37 provided at the same position as the cathode image formed between the first projection lens and the second projection lens and is sufficiently away from the optical axis. The second small hole (about 2 μm in diameter) 35
A second detector (Faraday gauge) for detecting an electron beam passing through the small hole 35 is formed below the small hole 35.
36 are provided.

The small hole provided at the same position as the above-mentioned cathode image and the detector provided below the small hole are connected to the cathode image formed between the second condenser lens and the illumination lens. They may be provided at the same position. Each of the detectors 26 and 36 is connected to the interface 9 and the CRT 27. Further, the deflectors 28, 3 provided above the molding opening 24 and the contrast aperture 37 are provided.
4 is connected to the CRT 27.

A specific operation procedure will be described using these configurations. First, the uniformity of the uniformity of the electron beam irradiated from the electron gun 21 is roughly adjusted. The electron beam is deflected by the second deflector 34 and scans the second small hole 35 in the X direction (horizontal direction in the drawing) and the Y direction (direction perpendicular to the drawing). The signal of the deflection amount of the electron beam deflected by the second deflector 34 and the signal of the electron intensity detected by the second detector 36 are CR
The electron beam is transmitted to T27 to derive from the deflection amount of the electron beam which position of the beam diameter, which is the cross section of the electron beam, has passed through the small hole 35. ) Is displayed.

For example, a person observes the electron intensity distribution displayed on the CRT 27 so that an optimal intensity distribution can be obtained (specifying a heater that needs voltage control among a plurality of heaters and examining the voltage value of the bombardment voltage). Perform an instruction from a computer connected to the interface 9). Since a cathode image is formed at this position, an intensity distribution having two peaks corresponding to the ring shape should be displayed.

Since the rotation amount (angle) of the electron beam by various lenses such as the first condenser lens 22 is calculated in advance, the electron beam is emitted from the electron emission surface 6 from the electron intensity distribution displayed on the CRT 27. The position of the heater 5 requiring voltage control is derived in consideration of the amount of rotation of the electron beam. Instructions from the computer are transmitted via the interface 9 to the bombardment voltage 8 of the heater 5 requiring voltage control.

When a predetermined electron intensity distribution is obtained by repeating such a series of operations, fine adjustment is performed next. In the fine adjustment procedure, the electron beam is deflected by the first deflector 28, scanned in the X and Y directions on the first small holes 25, and voltage control is necessary through the same process as the coarse adjustment described above. Such a series of operations is repeated until a suitable heater position is derived and a predetermined electron intensity distribution is obtained.

For example, when the electron intensity on the left side is low and the intensity on the right side is high, as in the electron intensity distribution shown in the CRT 27 shown in FIG. 2, the rotation amount (angle) of the electron beam is reduced. It can be seen that the temperature of the cathode surface at the position corresponding to the left side derived in consideration of the temperature is low and the amount of electron emission is small. Generally, the control of the electron gun as described above may be performed after the electron gun of the electron beam reduction transfer device is replaced. However, when the electron gun is unstable, the control is performed every time the mask (reticle) is replaced. Is preferred.

A human observes the image displayed on the CRT,
Instead of instructing the computer to make predetermined decisions,
A method of performing image processing on an RT image and directly sending the content calculated from the processing result to a computer may be employed.

[0027]

As described above, according to the electron gun of the present invention, since a plurality of heaters capable of independently controlling the voltage are provided on the back surface of the cathode, the mask is illuminated by controlling the voltage of each heater. The intensity of the emitted electron beam can be made uniform. Further, by arranging the heaters at substantially equal intervals radially from the center of the cathode back surface, it is possible to accurately control the uniformity of the electron beam intensity.

Further, by making the ring-shaped electron beam emitted from the electron emission surface, the influence of the space charge effect at the position where the cathode image is formed can be reduced.

[Brief description of the drawings]

FIG. 1A is a schematic sectional view of an electron gun according to an embodiment of the present invention, and FIG. 1B is a schematic bottom view.

FIG. 2 is a diagram schematically showing a configuration of an electron beam reduction transfer device using an electron gun according to the embodiment.

FIG. 3 is a diagram showing a change in current (electron emission amount) with respect to a change in temperature of a cathode of an electron gun having a predetermined potential difference between a cathode and an anode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Anode 2 ... Control anode 3 ... Cathode 4 ... Iridium film or rhenium film 5 ... Heater 6 ... Electron emission surface 7 ... Heating power supply 8 ... Bombard voltage 9 ... Interface 10 ... Support member 21 ... Electron gun 22 ... First condenser lens 23 ... Second condenser lens 24 ... Forming opening 25 ... First small hole 26 first detector 27 CRT 28 first deflector 29 illumination lens 30 mask (reticle) 31 first projection lens 32 Second projection lens 33 ... Photosensitive substrate 34 ... Second deflector 35 ... Second small hole 36 ... Second detector 37 ... Contrast aperture

Claims (4)

[Claims] 1. An electron gun comprising: a cathode having an electron emission surface; an anode for extracting electrons; and a heater for applying an electron impact to the back surface of the cathode, wherein the plurality of heaters are independently controllable in voltage. An electron gun, comprising: 2. The electron gun according to claim 1, wherein the plurality of heaters are arranged on the back surface of the cathode at substantially equal intervals radially from the center of the cathode. 3. The electron gun according to claim 1, wherein an electron beam (hollow beam) having a ring-shaped cross section is emitted from said electron emission surface. 4. A small hole provided in a plane including a nearby position where a cathode image or a crossover image is formed and sufficiently away from an optical axis, and a detector provided below the small hole. 4. The method for controlling an electron gun according to claim 1, which is used for an electron beam reduction transfer device having a deflector provided above the small hole, wherein the electron beam emitted from the electron gun is Deflection by a deflector, scanning over the small holes, detecting electrons passing through the small holes with the detector, and performing voltage control of the plurality of heaters based on an electron beam intensity distribution as a detection result. A method for controlling an electron gun.