Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
2000-03-23
2002-07-09
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C250S492100, C250S492200, C250S492220
Reexamination Certificate
active
06417516
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron beam lithographing method, in particular, to an electron beam lithographing method and an electron beam lithographing apparatus suitable for a large size of semiconductor integrated device and a high integration thereof.
2. Description of the Related Art
In recent years, as the size and integration of devices are becoming large, narrow exposed patterns are required. To satisfy that, a high throughput electron beam lithographing system has been proposed. An example of such a system is SCALPEL system. The SCALPEL stands for the SCattering with Angular Limitation in Projection Electron beam Lithography. In the electron beam lithographing system, each exposure field (stripe) (having a width of several millimeters) is scanned and exposed with a prepared electron beam (EB) mask. Thus, since the exposure stripes are connected, the connection adjusting method and the TAT (turn around time) thereof should be considered.
FIGS. 1A and 1B
are schematic diagrams showing the structure of a conventional SCALPEL type electron beam lithography apparatus.
In
FIG. 1A
, an electron beam radiated by an electron gun scans a strutted mask
11
that causes the electron beam to strut. The electron beam that passes through the strutted mask
11
is controlled by projector lenses
12
and
13
so as to form a lithography pattern corresponding to the mask on a semiconductor wafer
14
.
FIG. 1B
shows a feed-back operation of the apparatus. In
FIG. 1B
, the projector lens
12
and
13
has a SCALPEL aperture
121
and a beam deflecting portion
131
. A controlling system
16
controls the current, phase, and so forth of the beam deflecting unit
131
with the amount of beam detected by a BSE detecting portion
19
, an output signal of an interferometer
17
that detects the amount of beam and the position of the mask
11
, and an output signal of an interferometer
18
that detects the position of the wafer
14
. By scanning a focused electron beam to a photosensitive resist that is formed on a wafer that is a semiconductor substrate and then developing the resist, a predetermined resist pattern can be formed.
The mask and wafer are mechanically scanned through the illumination during an exposure in order to reach all patterned portions of the mask (FIG.
1
A). In order to achieve overlay, the positions of both stages area inter-fero-metrically monitored in real time. Relative stage position errors are determined and corrected using a stitching deflector. Such an error correction scheme is used in write-on-the-fly direct write systems, and has also been employed in electron beam proximity printers (P. Nehmiz, W. Zapka, U. Behringer, M. Kallmeyer and H. Bolen: J. Vac. Sci. & Technol. B3 (1985) 136).
FIG. 1B
shows, schematically, how this process works.
Previous attempts (M. B. Heritage: J. Vac. Sci. & Technol. 12 (1975) 1135; J. Frosien, B. Lischke and K. Anger: J. Vac. Sci. & Technol. 16 (1979) 1827); T. Asai, S. Ito, T. Eto and M. Migitake: Jpn. J. Appl. Phys. 19 (1980) 47) to construct high-throughput projection electron beam lithographing systems have utilized step-and-repeat writing strategies, which require that the electron optical system be capable of illuminating and projecting a mask area of at least one full die. The optical performance of these early systems was optimized, principally, by balancing diffraction effects against curvature of field (H. W. P. Koope: Microelectron. Eng 9 (1989) 217). Such an approach typically leads to the use of relatively small numerical apertures as a means of reducing aberrations. However, in order to achieve economically viable throughput levels, the beam current must be maximized, which means that electron-electron interaction effects must be considered (A. N. Broers and H. C. Pfeiffer: Proc. 11th Symp. on Electron Ion and Laser Beam Technology (San Francisco, 1971)). One of these effects is an uncorrectable image blur, which has a similar functional form to the diffraction limit, but whose magnitude is dependent on the beam current (L. R. Harriott, S. D. Berger, J. A. Liddle, G. P. Watson and M. M. Mkrtchyan: to be published in J. Vac. Sci. & Technol). When the type of full-field electron optical system previously considered is optimized taking this effect into account, it is found that the beam current must be held to impractically low levels in order to maintain acceptable resolution.
A related art reference for evaluating the accuracy of an electron beam lithographing process has been proposed as Japanese Patent Laid-Open Publication No. 59-124127. In the related art reference, an electron beam exposing pattern evaluating method is disclosed. In the electron beam exposing pattern evaluating method, an evaluation pattern is lithographed. An evaluation pattern area is disposed outside a real pattern area. An evaluation pattern is lithographed at intervals of a predetermined number of fields. By detecting the evaluation patterns, the lithography accuracy of the predetermined pattern is evaluated.
In the related art reference proposed as Japanese Patent Laid-Open Publication No. 59-124127, the evaluation pattern area is disposed outside the real pattern area. On the other hand, according to the present invention, an accuracy evaluation pattern is formed in a stripe connection boundary area. Thus, the technology of the related art reference proposed as Japanese Patent Laid-Open Publication No. 59-124127 is different from that of the present invention.
A related art reference for exposing a pattern with an electron beam has been proposed as Japanese Patent Laid-Open Publication No. 62-271424. In the related art reference, a charged beam exposing method is disclosed so as to form a pattern that connects fields with high accuracy. The charged beam exposing method comprises the steps of (a) exposing a pattern for measuring the accuracy of connections of fields, (b) forming a resist pattern for measuring the accuracy of the connections of the fields, (c) measuring the accuracy of the connections of the fields, and (d) inputting a compensation parameter to a deflecting unit of a charged beam exposing apparatus so as to expose a predetermined pattern.
In the related art reference proposed as Japanese Patent Laid-Open Publication No. 62-271424, the pattern for measuring the accuracy of the connections of the fields is exposed through a field boundary. On the other hand, according to the present invention, a pattern for evaluating the accuracy is formed in a stripe connection boundary area. Thus, the technology of the related art reference is different from that of the present invention.
A related art reference for exposing a pattern with an electron beam has been proposed as Japanese Patent Laid-Open Publication No. 6-204105. In the related art reference, an exposing method is disclosed so as to improve the overlap accuracy of the connected portion of adjacent shot areas. The exposing method comprises the steps of (a) exposing a transfer pattern image and an alignment mark image to a first shot area of a photosensitive substrate with a first mask having the transfer pattern and the alignment mark; (b) detecting the position of the alignment mark image when the first mask pattern image or a second mask pattern image is exposed in a second shot area corresponding to the first shot area on the photosensitive substrate in such a manner that the first mask pattern image or the second mask pattern image is connected to the transfer pattern image; and (c) aligning the mask of which the transfer pattern is formed in the second short area with the photosensitive substrate corresponding to the detected result.
In the related art reference proposed as Japanese Patent Laid-Open Publication No. 6-204105, when the first mask pattern image or the second mask pattern image is exposed in the second shot area, the alignment mark image that has been exposed is re-exposed. Thus, the alignment mark image that has been exposed and formed in the first shot area is erased. In the lithograph
Lee John R.
NEC Corporation
Vanore David A
Young & Thompson
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