Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-04-26
2002-12-17
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S398000
Reexamination Certificate
active
06495841
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a charged beam drawing apparatus for forming a fine element pattern for a semiconductor integrated circuit or the like on a substrate such as a semiconductor wafer or a pattern transferring mask by use of a charged beam, and more particularly to a charged beam drawing apparatus having a mechanism for mechanically moving an objective lens and objective deflector.
In an electron beam lithography in the semi-conductor manufacturing process, it is proved that the process to 0.01 &mgr;m can be attained by use of a finely converged beam. From the viewpoint of miniaturization, no problem will occur for the time being, but a problem occurs in the throughput as a device mass production tool. That is, in the electron beam lithography, since fine patterns are sequentially drawn one by one, the pattern drawing time becomes long. In order to reduce the drawing time, several devices such as a cell projection system for partially and simultaneously drawing a repeated pattern portion of a ULSI pattern are developed. However, it cannot catch up with the throughput of the optical lithography even by use of the above devices.
As one method for increasing the throughput of the electron beam lithography, an attempt is made to enlarge the deflection area of the objective deflector in the electron beam drawing apparatus and deflect the beam at high speed. In this case, the drawing throughput is enhanced, but since the deflection area becomes large, a degradation in the resolution occurs and the pattern will be distorted due to the lens aberration or deflection aberration. Therefore, the high precision drawing cannot be attained. Further, an electrostatic type deflector is used for deflecting the beam at high speed. The deflection area and a voltage applied to the electrostatic deflector have a preset relation, and if a voltage applied to the electrostatic deflector becomes high to deflect the beam to a large extent, it becomes difficult to deflect the beam at high speed.
Thus, in the prior art, in the electron beam drawing apparatus, if the deflection area of the objective deflector is enlarged to enhance the throughput, a degradation in the resolution occurs and the pattern will be distorted due to the lens aberration or deflection aberration, and therefore, the drawing with high precision cannot be attained. Further, it is difficult to cover the large deflection area by use of the high-speed deflectable type electro-static deflector. The above problem occurs not only in the electron beam drawing apparatus, but also in an ion beam drawing apparatus for drawing a pattern by use of an ion beam.
BRIEF SUMMARY OF THE INVENTION
This invention has been made in order to solve the above problem and an object of this invention is to provide a charged beam drawing apparatus capable of suppressing occurrence of distortion of a pattern and a degradation in the beam resolution caused by an increase in the deflection area and enhancing the throughput and drawing precision.
The above object can be attained by a charged beam drawing apparatus comprising a condenser lens for adjusting a charged beam emitted from a charged beam source to a desired size and brightness; an objective lens for focusing the charged beam on a sample surface; an objective deflector for controlling the position of the charged beam on the sample surface; a driving mechanism for mechanically moving the objective lens and objective deflector in a preset plane (for example, in a plane perpendicular to the optical axis of the charged beam); and an optical axis shifting deflector arranged nearer to the charged beam source than the objective lens and objective deflector, for deflecting the charged beam in synchronism with the operation of the driving mechanism.
Further, the above object can be attained by a charged beam drawing apparatus comprising a condenser lens for adjusting a charged beam emitted from a charged beam source to a desired current density; a character mask having a plurality of different aperture patterns, for selecting one of the aperture patterns to form a charged beam corresponding to the selected aperture pattern; an objective lens for forming an image on a sample surface based on the charged beam formed by the character mask; an objective deflector for controlling the position of the charged beam on the sample surface; a driving mechanism for moving the character mask, objective lens and objective deflector in a preset plane (for example, in a plane perpendicular to the optical axis of the charged beam); and an optical axis shifting deflector arranged nearer to the charged beam source than the character mask, for deflecting the charged beam in synchronism with the operation of the driving mechanism.
In the charged beam drawing apparatus, if the defection area by the objective deflector is enlarged, the deflection aberration becomes large and the beam orbit with respect to the objective lens is greatly deviated from the lens center, and as a result, the lens aberration becomes large. Therefore, in this invention, an attempt is made to mechanically move the objective lens and objective deflector in a direction perpendicular to the optical axis. Deviation of the axes of the objective lens and objective deflector from the optical axis caused by the mechanical movement of the objective lens and objective deflector is corrected by use of the optical axis shifting deflector provided in the preceding stage of the objective lens and objective deflector.
Therefore, according to this invention, since the total deflection area can be enlarged without enlarging the electrical deflection area by the objective deflector itself, the deflection aberration can be made small. Further, since the deflection area by the objective deflector itself is small, the lens aberration by the objective lens can be made small. Therefore, occurrence of the pattern distortion and the degradation in the beam resolution due to an increase in the deflection area can be prevented and the drawing precision can be made high together with the throughput. Particularly, this invention is effective when an electrostatic lens is used as the objective lens and an electrostatic deflector is used as the objective deflector in a low-acceleration electron beam drawing apparatus.
Further, a large number of opening patterns (aperture group) can be arranged in the mask by providing the driving mechanism for mechanically moving the forming aperture mask or character mask. As a result, the drawing throughput can be further enhanced.
Further, control for the mechanical movement of the objective lens and objective deflector can be made simple by controlling the driving mechanism to continuously change the moving speed of the objective lens and objective deflector. In addition, in a case where the driving mechanism is driven by use of a sinusoidal wave or the like, the beam is electrically deflected by the objective deflector in synchronism with the sinusoidal driving operation in order to compensate for a difference of the speed of movement by the driving mechanism with respect to a constant reference speed. As a result, a lowering in the throughput caused by using the sinusoidal wave for driving the driving mechanism can be suppressed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 4376249 (1983-03-01), Pfeiffer et al.
patent: 4827127 (1989-05-01), Todokoro
patent: 4963748 (1990-10-01), Szilagyi
patent: 5153441 (1992-10-01), Moriizumi
Eiichi Goto and Takashi Soma “MOL (moving objective lens) Formulation of Deflective Aberration Free System” Optik 48 No. 3, p. 255-270, 1977.
Ando Atsushi
Hattori Kiyoshi
Magoshi Shunko
Miyoshi Motosuke
Okumura Katsuya
Berman Jack
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
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