JPH0314219A - Electron beam lithography device - Google Patents

Abstract

PURPOSE:To enable the beams to be automatically focussed regardless of the size and variation of beam current density thereby enhancing the lithographic precision and the operating efficiency of the title device by a method wherein the correcting coefficient for correcting the slip in focal point of beams as a function of current is previously stored in a memory. CONSTITUTION:Within the title electron beam lithography device in variable forming beam system provided with a zoom lens comprising at least two condenser lenses 11, 12 zooming out a crossover on an electron gun 10 to focus the crossover on a beam limiting aperture; variable zooming magnification means of zooming lens corresponding to the specific current density J; and a correcting means of the slip in focal point of beams forms a specimen 20, the purpose of the slip correcting means 11 is to correct the slip DELTAt defined as the product DELTA of a coefficient p(J) defined as a function of beam current density J and a beam sectional area (a) i.e., the product DELTA=p(J).a while the functional formula for calculating the coefficient p(J) shall be previously stored in a memory 34.

Description

Detailed Description of the Invention [Invention 1] (Industrial Application Field) The present invention relates to an electron beam lithography system using a variable shaped beam method, and in particular to an electron beam lithography system with an improved focus correction means. Regarding.

(Conventional technology) In recent years, with the progress of LSI development, the miniaturization of LSI patterns has become remarkable, and the development of advanced devices requires lithography technology in the 0.3 to 0.1 μm range, which is difficult to use with normal optical lithography technology. It has come to be that. Currently, electron beam lithography equipment is used for LSI in this area.
It is the only reliable lithography tool that can create patterns. Lithography equipment used in the device development process is required to have high processing speed.

For this purpose, a variable shaped beam type electron beam lithography apparatus has recently been proposed and used.

FIG. 4 shows the optical system configuration of a conventional variable shaped beam type electron beam lithography apparatus. In the figure, 1 is a first shaping aperture, 2 is a second shaping aperture, 3 is a projection lens for projecting the image of shaping aperture 1 onto shaping aperture 2, and 4 is a shaping aperture for projecting the image of shaping aperture 1 onto shaping aperture 2. 2 is a deflector for moving on the sample surface, 5 is an objective lens for projecting the shaped aperture image combined by the shaping apertures 1 and 2 onto the sample, and 6 is a deflector for positioning the beam on the sample surface. , 7 is a limiting aperture for limiting the beam.

An electron beam drawing device equipped with such an electron optical system is
Since the cross-sectional shape of the beam is changed according to the pattern data and the beam is moved, the beam current changes dynamically during writing.

For this reason, the Coulomb interaction force between electrons in the beam changes, resulting in a disadvantage that the focal position of the beam relative to the sample shifts dynamically and the beam becomes blurred. Generally, this focal shift ΔZ is expressed as ΔZ=k−L·1·α−·····■. Here, k is a constant and L is the optical path length.

l is the beam current and α is the beam convergence half angle.

Due to the focal shift of ΔZ, the beam becomes δ=2αΔZ . . . ■ The blur will increase. Therefore, in the past, a method was adopted in which the device was used within an allowable range of blur, that is, a method was used in which the beam current was limited.

However, this method has a low throughput because it limits the amount of irradiation per unit time, that is, the amount of processing. Therefore, recently, instead of limiting the beam current, a new focus correction lens has been installed, the beam current of each point, that is, the beam cross section is calculated from the drawing pattern data, ΔZ is predicted and calculated in advance, and ΔZ is corrected. A method was proposed in which the focus shift of bamboo is corrected using a correction lens (Morit
a and others, former crocircujt lngineerin
g 85°ed, Van der Mast,
North-Holland, Amsterd
am1985 p53).

When this method is applied to the optical system shown in FIG. 4, the following problems arise. Generally, when manufacturing a device by electron beam lithography, it is necessary to select a resist suitable for the underlying material to be etched. Furthermore, it is desirable to perform writing by setting the optimum current density after considering the sensitivity of the resist, its resistance to heat increase caused by irradiation, and the writing processing speed. For this purpose, the optical system shown in FIG. 4 makes it possible to change the current density using condenser lenses CL1 and CL2. That is, CLI and CL2 work as a zoom lens, and the electron gun crossover Q, which is a light source,
is enlarged and imaged onto the limiting aperture. This method changes the current density by changing the expansion rate of the crossover Q. In this method, in a region where the current density is low, the relationship ΔZ=p-a...■ holds true. However, p is a constant (correction coefficient).

a is the beam cross-sectional area. However, it was found that when the current density is high, this relationship does not hold because the beam is limited by the limiting aperture, and p changes with respect to the current density. In other words, it has been found that there is a problem in use that the correction coefficient p must be reset every time the current density is changed.

(Problem to be Solved by the Invention) In this way, with the conventional method of correcting beam defocus according to the beam cross-sectional area, if the beam current density is low, is it possible to accurately correct the deviation? When the current density is high, it is not possible to accurately correct the deviation by changing the current density, resulting in a problem of lowering the drawing accuracy. Furthermore, in order to perform accurate deviation correction even when the beam current density is high, it is necessary to reset the correction coefficient p every time the current density is changed, which causes a decrease in the device operating rate.

The present invention has been made in consideration of the above circumstances, and its purpose is to
It is an object of the present invention to provide an electron beam lithography apparatus that can automatically focus the beam even when the current density is changed, and that can improve the lithography accuracy and the operating rate of the apparatus.

[Configuration of the Invention (Means for Solving the Problems) The facet of the present invention stores a correction coefficient for beam defocus correction in a memory in advance as a function of current density, and changes and sets the current density. The purpose is to automatically adjust the value of this function by determining the value of this function at each time, and resetting this value as a correction coefficient.

That is, the present invention includes a zoom lens that is composed of at least two condenser lenses and that magnifies the electron gun crossover to form an image on the beam limiting aperture, and a zoom lens that varies the magnification magnification of the zoom lens in accordance with the desired current density J. Based on the means and beam data defining the dimensions and shape of the beam,
In a variable shaping beam type electron beam lithography apparatus equipped with a means for correcting a deviation ΔZ defined by the product ΔZ=p−a of the coefficient p and the beam cross-sectional area a, the coefficient p is set by the beam current density J. The coefficient p (J) is defined as a function p (J), and means is provided for previously determining and storing a functional formula for determining the coefficient p (J).

(Function) According to the present invention, by expressing the correction coefficient as a function of the beam current density, it is possible to set the correction coefficient with high precision regardless of changes in the current density, and as a result,
The usable beam current range can be expanded. Furthermore, there is no need to manually reset the correction coefficient every time the current density is changed, and the correction coefficient is automatically set, so it is possible to improve the device operating rate.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic 114 diagram showing an electron beam lithography apparatus according to an embodiment of the present invention. In the figure, 10 is an electron gun, and the crossover of this electron gun 10 is irradiated onto the first shaping aperture 13 via the first and second condenser lenses 1]-12. Here, the crossover is the lens]
112, the objective lens]
7 beam-limiting apertures. The image of the shaping aperture 13 is projected onto the second shaping aperture 15 by the projection lens]4, and an optically overlapping image of the shaping aperture 13.15 is imaged onto the sample 20 via the reduction lens 16 and the objective lens 17. , and is further scanned by a scanning deflector 18.

An aperture 21 for focusing is arranged between the condenser lens 12 and the shaping aperture 13, and a deflector 22 for focusing and a backscattered electron detector 23 are arranged between the lens 12 and the aperture 21. ing. A deflector 24 is arranged between the shaping apertures 13.15 for varying the optical overlap of the apertures 13.15. A correction lens 25 for focusing and a deflector 26 for position correction are arranged between the lenses 1, 6 and 17. A backscattered electron detector 27 is arranged between the lens] 7 and the sample 20. Further, a particle mark 28 for beam detection is provided on the surface of the sample 20, and a Faraday cup 29 is further provided for beam current detection.
is provided.

On the other hand, 30 in the figure is a CPU for various controls.

31 is a magnetic disk for storing drawing data, 32 is a terminal such as a keyboard, 33 is a beam data generation circuit, 34 is a memory for storing a correction coefficient p, 35 is a position correction circuit, and 36 is a correction lens control circuit. ing.

The operation of the apparatus configured as described above will be explained with reference to flowchart 1 in FIG.

First, the required current density J is determined after considering various requirements such as resist sensitivity, heat resistance, and writing processing speed. Start the current density setting program from the terminal 32 and input the current density J.

The excitation current 1112 of the condenser lenses 11, 1.2 is J
It is expressed as a function of and is set by the CPU 30. Aperture 2 due to lens hysteresis
Since the focus shifts relative to 1, the deflector 22 scans the beam over the aperture 21, and the amount of shift is determined from the detection signal of the detector 23. Then, based on this amount of deviation, the excitation current 12 of the lens 12 is finely adjusted to accurately focus on the aperture 21. Although not shown in the figure, various necessary axis alignment adjustments are also performed.

After focusing on the aperture 2], the beam current is determined as a function of the beam size using the Faraday cup 29, and the current density is confirmed. If necessary, make correction adjustments and complete the current density setting. Subsequently, a correction coefficient p for the input current density J is calculated using the coefficient p(J) as a function of current density, and this is set in the memory 34.

Test data is sent to the beam data generation circuit 33, the excitation current 13 of the correction lens 25 is changed, the mark 28 is scanned by the deflector 18, and the beam position is detected by the detection signal of the detector 27.

Changes in beam position due to changes in beam data, that is, i3, are detected by the above means, and if the position shifts, the movement vector is determined as a function of the beam data, and reverse correction is made to the beam data so that the amount of shift becomes zero. The coefficients for carrying out the process are calculated based on and set in the memory 34. The adjustment is thus completed.

When drawing, the CPU 30 stores the drawing data in the storage device 3.
The data are read out sequentially starting from 1 and a portion is sent to the beam data generation circuit 33. The beam data generation circuit 33 generates data on the shape and dimensions of the beam according to a pre-designed procedure based on the data, and the position correction circuit 35 and the correction lens control circuit 36
send to At the same time, a trigger is issued to the memory 34.

The respective correction coefficients are sent from the memory 34 to a position correction circuit 35 and a correction lens control circuit 36, and control signals for the correction lens 25 and deflector 26 are calculated. At the same time, a signal is also sent from the beam data generation circuit 33 to the deflector 24, whereby a precisely focused beam is irradiated onto the sample surface.

Here, the focus correction is defined as the product ΔZ=p (J) ・a ......■ of the coefficient p (J) defined as a function of the beam current density J and the beam cross-sectional area a. The amount of deviation ΔZ is corrected by the correction lens 25, and it becomes possible to always maintain focus regardless of changes in current density and beam cross-sectional area.

Since the function p (J) varies depending on the configuration of the electron optical system, electron gun characteristics, and accelerating voltage, it is measured in advance and stored as a function of J on the magnetic disk. For example, in the configuration of the optical system as shown in Fig. 4, the cathode tip diameter is 80 μm.
Accelerating voltage 20k using electron gun with a86 cathode
eV te movement] 3 If made, as shown in Figure 3, J > IOA / c
It deviates from the straight line in the area of m2. For example, J=10
At 0A/cm2, in the conventional method ΔZ/ΔI = 0
．． This results in an error of 3 μm/μA. Therefore, if the maximum beam dimension is shifted by 5 μm, I = l0ox (5x
lO-') 2=25μAΔZ=0.3X 2
This means that a focal shift of 5=7.5 μm has occurred. In the present invention, the measured values shown by the solid line in FIG.
) is approximated in the form. a...e are coefficients, and n is an index.

Note that although the above description does not mention where the origin of correction should be set, it may be any position within the allowable range of correction error. For example, the objective lens 17 may be focused on a beam having an area of 1/2 of the maximum beam area, and this may be used as the correction origin. In this case, the maximum amount (absolute value) of the amount of correction by the correction coil can be reduced. In addition, LS containing fine patterns of about 0.1 μm
When drawing an I pattern, it is desirable to use the focal point of a beam of minute dimensions corresponding to a fine pattern with strict precision as the origin.

Thus, according to this embodiment, by expressing the correction coefficient p for correcting the focal shift that occurs when changing the beam size as a function p (J) of the current density, high precision can be achieved for the required current density. It is now possible to set the correction coefficient p, and as a result, it is possible to improve the drawing accuracy. Furthermore, since the correction coefficient p can be set accurately even when the current density becomes high, the usable beam current range can be expanded. Further, since the correction coefficient is automatically set without the need to manually reset the correction coefficient every time the current density is changed, it is possible to improve the device operating rate.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the configuration of the electron optical system is not limited to the same as shown in Fig. 15, but may be a system in which at least two condenser lenses are used as zoom lenses and an electron gun crossover is imaged on a limited aperture. Bye.

[Effects of the Invention] As detailed above, according to the present invention, a correction coefficient is stored in the device in advance as a function of current density, and each time the current density is changed, the value of this function is determined, and the correction coefficient is Since the beam is automatically adjusted to reset the settings, the beam can be focused automatically regardless of the beam current density, improving writing accuracy and equipment operating rate. .

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an electron beam lithography apparatus according to an embodiment of the present invention, Fig. 2 is a flowchart for explaining the operation of the above-mentioned apparatus, and Fig. 3 shows the relationship between current density and deviation amount. The characteristic diagram shown in FIG. 4 is a diagram showing the optical system configuration of a conventional electron beam lithography apparatus. ] 6 10・Electron gun, 11,. 12... Condenser lens (zoom lens), 13.15.21... Aperture, 14... Projection lens, 16... Reduction lens, ]7... Objective lens, 18.22, 24.26...・Deflector, 20... Sample, 23.27... Backscattered electron detector, 25... Correction lens, 28... Mark (fine particles), 2... Faraday cup, 30... CPU . 3]...Magnetic disk, 32.Terminal, 33.Beam data generation circuit, 34.Memory, 35.Position correction circuit, 36.Correction lens control circuit. 7

Claims (2)

[Claims] (1) A zoom lens consisting of at least two condenser lenses, which magnifies the electron gun crossover and forms an image on the beam limiting aperture, and means for varying the magnification of the zoom lens according to the desired current density J. , and means for correcting a shift in the focus position of the beam relative to the sample based on beam data that defines the size and shape of the beam, the means for correcting the shift comprising: It corrects the deviation ΔZ defined by the product ΔZ of the coefficient p(J) defined as a function of the beam current density J and the beam cross-sectional area a, ΔZ=p(J)・a, and the coefficient p(
An electron beam lithography apparatus characterized in that a functional formula for determining J) is preset in a memory. (2) The correction origin when correcting the deviation ΔZ is set to the focal point of a beam with an area of 1/2 of the maximum area, or the focal point of a beam corresponding to the minimum dimension of the pattern to be drawn. An electron beam lithography apparatus according to claim 1.