Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
1999-04-15
2003-01-21
Anderson, Bruce (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S491100
Reexamination Certificate
active
06509564
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a workpiece holder for holding a workpiece such as a semiconductor wafer, a semiconductor fabricating apparatus having the workpiece holder, a semiconductor inspecting apparatus, a circuit pattern inspecting apparatus, a charged particle beam application apparatus, a calibrating substrate, a workpiece holding method, a circuit pattern inspecting method, and a charged particle beam application method.
BACKGROUND OF THE INVENTION
With the trend toward finer-geometries of circuit-patterns of semiconductor wafers, a circuit pattern inspecting apparatus employing electron beams has come to be put into practical use.
Techniques concerning such a circuit pattern inspecting apparatus have been described, for example, in Japanese Patent Laid-open No. Sho 59-192943, Japanese Patent Laid-open No. Hei 05-258703, Sandland, et al., “An electron-beam inspection system for x-ray mask production”, J. Vac. Sci. Tech. B, Vol.9, No.6, pp.3005-3009 (1991), Meisburger, et al., “Requirements and performance of an electron-beam column designed for x-ray mask inspection”, J. Vac. Sci. Tech. B, Vol.9, No.6, pp.3010-3014 (1991), Meisburger, et al., “Low-voltage electron-optical system for the high-speed inspection of integrated circuits”, J. Vac. Sci. Tech. B, Vol.10, No.6, pp.2804-2808 (1992), Hendricks, et al., “Characterization of a New Automated Electron-Beam Wafer Inspection System”, SPIE Vol. 2439, pp.174-183 (Feb. 20-22 1995).
To inspect a circuit pattern, which comes to be formed in finer-geometries on a wafer having an increased diameter, highly accurately at a high throughput, it is necessary to acquire a pattern image with a higher SN ratio at a very higher speed. To satisfy such a requirement, it is required to keep a higher SN ratio by ensuring the necessary number of electrons to be emitted to the circuit pattern using a large current beam which is equal to or more than 100 times (10 nA or more) that used for a usual scanning electron microscope (SEM), and further, it is essential to highly efficiently detect secondary electrons produced from a substrate and reflection electrons reflected therefrom at a higher speed.
On the other hand, to prevent a semiconductor substrate having an insulating film such as a resist from being affected by electrification, the semiconductor substrate is irradiated with a low acceleration electron beam of 2 KeV or less. The technique is described on pages 622-623 in “Electron and Ion Beam Handbook” 2nd Edition, edited by 132nd committee of Japan Society for the Promotion of Science, published by Nikkan Kogyo Simbun, Ltd. (1986). A large current and low acceleration electron beam, however, makes it difficult to observe a circuit pattern at a high resolution because it produces aberration due to the space-charge effect.
A method of solving such a problem has been known in which a high acceleration electron beam is retarded directly before a workpiece to irradiate the workpiece with a substantially low acceleration electron beam. The technique has been described, for example, in Japanese Patent Laid-open Nos. Hei 02-142045 and Hei 06-139985.
The outline of one example of an electro-optical system of a prior art circuit pattern inspecting apparatus will be described below with reference to FIG.
9
.
FIG. 9
is a schematic view of an electro-optical system of the prior art circuit pattern inspecting apparatus.
A primary electron beam
201
emitted from an electron gun
1
with a voltage applied to an extraction electrode
2
passes through a condenser lens
3
, a scanning deflector
5
, an aperture
6
, an objective lens
9
and the like to be converged and deflected onto a substrate
10
for a semiconductor device placed on workpiece stages
11
and
12
. To retard the primary electron beam
201
, a retarding voltage is applied from a high voltage power source
23
to the substrate
10
. The irradiation of the substrate
10
with the primary electron beam
201
produces secondary electrons
202
from the substrate
10
. The secondary electrons
202
are accelerated to an energy of several KeV by the retarding voltage. An EXB deflector
8
is provided on the electron gun side of the objective lens
9
in such a manner as to be adjacent to the objective lens
9
.
The EXB deflector
8
is adapted to cancel the deflection amounts of the primary electron beam
201
due to an electric field and a magnetic field each other and to deflect the secondary electrons
202
by superimposition of the deflection amounts of the secondary electrons
202
due to the electric field and magnetic field. The accelerated secondary electrons
202
thus deflected by the EXB deflector
8
is attracted by an electric field formed by an attraction voltage applied between a detector
13
and an attraction electrode
14
mounted around the detector
13
, to enter the detector
13
.
The detector
13
is configured as a semiconductor detector. The secondary electrons
202
having entered the semiconductor detector produce electron-positive hole pairs which are then taken out as a current to be converted into an electric signal. The output signal is amplified by a pre-amplifier
21
, to become a brilliance modulation input for forming an image signal. After an image of one region of the substrate is acquired by the above operation of the electro-optical system, the image output signal is delayed for a time corresponding to one image plane, and then an image of a second region is similarly acquired. These two images are compared with each other by an image comparing/evaluating circuit, to thus detect a defective portion of the circuit pattern. Here, the irradiated position with the primary electron beam
201
is determined as a position of the substrate on which the electron beam is impinged on the basis of a scanning-deflection signal inputted in the scanning deflector
5
.
If the surface height of the substrate is varied by warping of the wafer or the like, however, the irradiated region of the substrate with an electron beam is substantially varied although the electron beam is scanned on the basis of the same deflection signal, that is, the same beam deflection cannot be obtained between two irradiated regions of the substrate.
To solve such a problem, a prior art electron beam application apparatus such as an electron beam plotting apparatus has adopted the following deflection correcting manner:
(1) A sample with standard marks formed on at least two surfaces different in thickness is provided at the outermost peripheral portion of a workpiece stage, and a positional offset between image signals obtained from the standard marks having the different heights is calculated.
(2) The height of each standard mark is converted into a signal by operating an optical sensor for successively measuring the surface height of the workpiece.
(3) A deflection correcting table corresponding to the height is calculated on the basis of the height signal of each standard mark and the positional offset between image signals of the standard marks. The deflection correcting table is stored, and upon observation of the substrate, the deflection is corrected by calculating a deflection correcting signal corresponding to the surface height of the substrate on the basis of the deflection correcting table.
With this technique, even if the surface height of a substrate is varied by warping of the wafer or the like, two regions of the substrate which are different in surface height can be equally irradiated with an electron beam on the basis of a corrected deflection signal.
The technique has been described, for example, in Japanese Patent Laid-open No. Sho 56-103420. According to this technique, the deflection correcting table can be simply updated by repeatedly observing the standard marks provided at the(outer peripheral portion of the workpiece stage on which the wafer is left mounted. As a result, even if there occurs a drift of the deflection amount of a primary electron beam due to the change in the electro-optical system with the elapsed time, the deflectio
Shinada Hiroyuki
Sugiyama Shuji
Suzuki Hiroyuki
Takafuji Atsuko
Usami Yasutsugu
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