A new resistor network for an electrostatic octupole deflector combined with a
stigmator
T. Ohnishi, S. Hosaka, H. Tamura, T. Ishitani, and T. Noda
Citation: Review of Scientific Instruments 62, 240 (1991); doi: 10.1063/1.1142321
View online: http://dx.doi.org/10.1063/1.1142321
View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/62/1?ver=pdfcov
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A new resistor network for an electrostatic
a stigmator
octupole
deflector
combined
with
T. Ohnishi, S. Hosaka, H. Tamura,a) and T. lshitani
Central Research Laboratory, Hitachi, Ltd., Kokubunji,
Tokyo 185, Japan
T. Noda
Toyohashi University of Technology, Tempaku, Toyohashi 440, Japan
(Received 6 August 1990; accepted for publication 22 August 1990)
A new resistor network for an octupole deflector combined with a stigmator is proposed.
Improvement on the time constant due to the octupole’s stray capacity, which is made by
connecting phase-compensative capacitors parallel to the resistors, is also described.
Electrostatic octupole deflectors’,* are used in a variety
of electron- or ion-beam systems such as the scanning electron microscope (SEMI and the focused ion-beam (FIB)
apparatus. In some systems, 3*4deflection potentials superimposed on stigmation potentials have been applied to the
octupole so that simultaneous deflection and astigmation
can be obtained. A resistor bridge’ is a simple method to
provide the necessary potentials for all octupole segments,
but its application has been restricted only to the deflectors.
In the present paper a new resistor network is proposed for a
dual-purpose deflector and stigmator.
A cross sectional configuration of the octupole segments
and the proposed network are shown in Figs. 1 (a) and 1 (b),
respectively. Here, R ,, RP, R, and r are precision resistors,
+ V, and + V,, are the master deflection potentials, and
& S, and + S, are the master stigmation potentials. The
potential F. applied on the ith electrode (i= 1-8) is supplied from the ith node in the network. The V, values are
given by
v, = K, v, + K,S,,
v* = K, ( v, + v, ) - K4S*,
The octupole, which is symmetrical about the x = 0, y = 0,
and x = y directions, satisfies the equation
K/&I,
= 1/2’f2.
(3)
Here, the K, value represents the deflector sensitivity with
regard to V, and V,. Similarly, the K3 and K4 values represent the stigmator sensitivities with respect to S, and S,,
respectively. For example, in the case of r = R (i.e., K, = I/
3 = 0.333), K, = 2”‘/3
( = 0.471), and in the case of
yey
5
1
(-I--)
8
X-T
(4
7
V;=K,V,--K,S,,
- v, + v,,
V,=K,(
v,=
-K,I/,
vb=K*(
v,=
+K,s,,
f&S,,
- v, - v,,
-K,Vy
Vx=K,(V,
-K4&,
-KJ,,
- F(y) +K4s_‘,
(1)
where
K, = R,/(R,
+&I
KS = R,/(R,
+&I
,
( = 1 - K,),
K,=r/(2r+R),
K4= R/(2r+
(=l-2K*).
R)
(2)
“Presently at Hitachi Instrument Engineering Co., Ltd., 882 Ichige, Katsuta-Shi, Ibaraki, Japan.
(b)
-W
FIG. 1.Octupoledeflectorandresistornetwork:(a) a cross-sectional
configuration of the octupole and (b) the resistor network for an octupole deflector combined with the stigmator.
240
Rev. Sci. Instrum. 62 (1), January 1991
00346?48/91/010240-02$02.00
0 1990 American Institute of Physics
240
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VI:
vx
R
R!
VY
,
w
RI
G
I
.cl
Ia)
G
0
R
R
VX
G
_ - _-__--__
k
R2
G
r
T
I
(b)
Cd
I
ICI
FIG. 2. Equivalent load circuits of the V, driver and their phase-compensation circuits: (a) equivalent load circuit of the V, driver, (b) the phasecompensation circuit of (a), and (c) phase-compensation circuit of the V2
driver.
r = 6R
(i.e.,
K, = 6/13 = 0.462),
K, = 6x2”*/13
( = 0.653).
Next, consider the application of the network to highfrequency voltage scan. The maximum frequency is determined as a function of the output resistance R, and capaci-
FIG. 3. Resistor network for high-frequency voltage-scan octupole.
tance C,. Here, C, represents the small stray capacitance
between the octupole segment and the grounded conductor.
Figure 2(a) shows an equivalent load circuit for the I’, driver. The V, driver has the time constant T,, where T, = R, Cd
and R e- ’ = R ; ’ + R ; ‘. The quick responsein V, (i.e., T,
= 0) is achieved by connecting in parallel a phase-compensative capacitor C, to the resistor R ,. The C, value is determined from an equilibrium condition of V, = V, on a bridge
circuit as shown in Fig. 2 (b). Then, the condition rewritten
as R ,/C, = R2/CB leads to C, = (RJR, ) C,. Similarly, for
Vz, T, = R,C, and R em’ = r- ’ + 2R - ‘. The phase-compensative capacitor C, connected to each resistor R as
shown in Fig. 2(c), is determined from the rewritten condiwhere
R R, ’
tion
of
R/CC, + Cd) = R,,/C,,
= R - ’ + r- ‘, and it results in C, = (r/R ) C,. Finally, the
improved network is achieved as shown in Fig. 3.
It is desirable for all resistors in the network to be in a
common environement so that the temperature coefficients
of their resistivities will not affect their ratios in Eq. (2)) and
the thermal drift on Vi can be reduced. A thin-film resistor
network is one example of a suitable network. Although the
proposed network has deflection sensitivity loss, the superposition of the deflection voltages and the stigma voltages
does not require any more operational amplifiers (at least
eight OP amps) having inherently an offset voltage, drift,
and noise. Since there are not any active elements such as an
OP amp, the network is also easily operable for a highervoltage drive. The present network is applicable for both
superposition of an octupole stigmator on an aligner as well
as an octupole deflector on an aligner. Furthermore, its application can be expanded for multipole deflectors such as
for 12, 16, and 20 pole deflectors.
‘J. Kelly, Adv. Electron. Electron Phys. 43, 43 ( 1977).
‘E. F. Ritz, Jr., Adv. Electron. Electron Phys. 49, 299 (1979).
‘M. M. ElGomati, M. Prutton, and R. Browing, J. Phys. E 18,32 ( 1985).
‘T. Ohnishi, T. Okutani, K. Hata, H. Ohiwa, and T. Noda, J. Vat. Sci.
Technol. B 4, 143 (1986).
Notes
241
241 is copyrighted
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Vol. in
62,the
No.article.
1, January
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