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```and one 8-bit register to retain the result, and also the execution time is speeded up. When the multiplier is a 8-bit number,
eqn. 3 could be easily modified by removing (P328) from it.
When it is a 16-bit number, (P^12) must be added to the
equation and P 4 = - 8 x i 5 + 4 x i 4 + 2x 13 + lx 12 + lx n .One
can see, from the demonstrated example, that the e.b.a. is wel.
suited for a subroutine since it always takes afixednumber ol
shifts and additions to perform the multiplication. To do this,
number of cycles using e.b.a. = 106 x 10 = 1060. The total
storage (bytes) = 10 x 25 + 39 = 289.
The gain using e.b.a. is 1460 — 1060 = 400 clock cycles at
the expense of 263 bytes of program storage. However, this is
the worst case value, and all 10 coefficients will noi fall in this
category in a practical case. The e.b.a. is clearly superior when
speed is the primary concern, although it consumes much more
memory space.
Table 1
12-bit coefficient
in 2's complement
0
0
1
1
1
1
1
0
0 0
10
0 0
10
1 1
10
0 0
0 0
0 0
10
0 0
0 1
10
10
0 1
10
0 10 0 1
10 10 1
0 0 10 0
10 0 1 1
0 0 10 1
10 0 10
0 10 10
0 0 10 0
Type of
coefficient
0 0
0 1
10
0 0
0 1
0 1
10
0 1
Required number
of clock cycles
of clock cycles
(e.b.a.)
(m.m.i.)
87
89
91
90
92
99
103
82
146
146
146
146
146
146
146
146
Positive
Positive
Negative
Negative
Negative
Negative
Negative
Positive
and {Piyio) are calculated in the main program and these values are then transferred to the subroutine,
where the result is obtained.
Assume a digital filter is to be implemented on Intel 8086
with 10 multiplications. The coefficients and data words are
12-bit numbers. The m.m.i. takes 146 clock cycles2 to perform
12 x 12 bit signed multiplication. The total number of cycles
using m.m.i. is 146 x 10 = 1460. The total storage = 26 bytes
(coefficient storage and for instructions).
If the implementation is done using e.b.a., then calculation of
(Piyio), (Pzyio) and (P 3 yi 0 ) takes 30 clocks and 25 bytes
storage in the worst case. The subroutine takes 41 clock cycles
and 39 bytes storage. The call & ret. instruction (within
segment) takes 35 clock cycles. Therefore, under worst conditions, one multiplication takes altogether 106 clocks. The total
PULSED ELECTRON-BEAM ANNEALING OF
PHOSPHORUS-IMPLANTED SILICON
Indexing terms: Annealing, Electron-beam effects, Phosphorus,
Silicon
Electrical properties of phosphorus-implanted silicon annealed by a single shot of a high-power pulsed electron beam
have been studied by differential Hall-effect and sheetresistivity measurements. Nearly 100% electrical activation of
implanted phosphorus can be obtained after electron-beam
annealing at an incident energy density of 0-92 J/cm2. Uniformly distributed carrier concentration profiles have been
formed by electron-beam annealing.
Beam annealing using either pulsed1"3 or scanned45 electron
beam has recently received much interest as an alternative
technique for regrowth of implantation-induced amorphous
layer and electrical activation of implanted species. At present,
however, published data of detailed electrical evaluation on
ion-implanted and electron-beam-annealed semiconductors
are limited. In this work we will report doping profiles for
P+-implanted Si after a single shot of a pulsed electron beam.
The effect of additional thermal annealing on the doping
profile of electron-beam-annealed samples is also presented.
P + ions-were implanted into (lOOjhoriented p-type single
crystal Si (p = 80-100Qcm) to a dose of 50 x 1015/cm2 at an
incident energy of 120 keV and at room temperature. The Si
wafer was tilted 7° from the incident ion beam to reduce axial
channeling. The implanted layer was found to be transformed
to an amorphous state, which was determined by a glancingangle electron diffraction examination. After implantation
samples were annealed by a single shot of pulsed electron beam
in vacuum. The mean electron energy was 20 keV with a maximum energy less than 40 keV, which is sufficiently lower than
54
Required number
Table 1 gives the comparison between e.b.a. and m.m.i. for
some filter coefficients.
30th November 1979
E. AMBIKAIRAJAH
M. J. CAREY
University of Keele
Keele, Staffordshire, ST5 5BG, England
References
1
RABINER, L. R., and GOLD, BERNARD: Theory and applications of
digital signal processing'
2 Mcs-86 Users Manual, Intel, July 1978
0013-5194/80/020053-02\$! .50/0
the threshold energy for Si displacement (145 keV) in single
crystal Si.6 The electron pulse width was approximately 50 ns.
The incident energy density was 0-92 or 117 J/cm2. Note that
no cracks and ripples were detected on the surface of samples
after electron-beam annealing. Some of the electron-beamannealed samples were additionally annealed for 20 min at
temperatures between 300 and 1000°C.
1021
i
TO
X)
01
02
03
04
depth, jjm
05
06
10
Fig. 1 Carrier concentration (n) mobility (/i) profiles for P+-implanted
(5 x 1O1S cm'2) silicon samples. A and O: samples annealed by
electron-beam irradiation at an energy density of 1-17 and 0-92 J/cm2,
respectively. # : sample annealed by electron-beam irradiation at 0-92
J/cm2 and then annealed isochronally from 300 to 1000°C at 100°C
interval
ELECTRONICS LETTERS
17th January 1980
Vol. 16 No. 2
The van der Pauw configuration was formed on annealed
samples by a standard photoresist technique. Carrier concentration and mobility profiles were examined by successive
Hall-effect and sheet-resistivity measurements combined with
anodised layer stripping. The anodisation of the Si was carried
out in a solution of ethyleneglicol and 0-04N KNO 3 under a
constant current condition. Electrical contacts on annealed
samples were made by evaporating gold at room temperature.
Fig. 1 shows typical carrier concentration and mobility
profiles obtained from samples annealed at energy densities of
0-92 and 112 J/cm2. Atomic concentration profile predicted by
the l.s.s. range-energy theory7 is also given with a dotted line in
Fig. 1. Differing from the Ls.s. profile, carrier concentrations
for the two samples (0-92 and 112 J/cm2) were fairly constant
from the implanted surface to around 0-25 fxm at a doping level
of 1-6 x 1020 and 2 x 1020 /cm3, respectively. Moreover, no
distinct difference in the shape of doping profile could be observed between those two samples. In the deeper part of
profiles, carrier concentrations decreased rapidly (Fig. 1). Similar uniformly distributed profiles have been reported for both
pulsed-laser and electron-beam-annealed Si and GaAs where
liquid regrowth of the implantation-induced amorphous layer
occurs during annealing.3'89 The total number of carriers in
the P+-implanted layer was found to be « 5 x 1015/an2 for
both samples annealed at energy densities of 0-92 and 112
J/cm2, which was obtained by the integration of measured
profiles shown in Fig. 1. This result shows that a 100% electrical activation of implanted P atoms can be obtained by a single
shot of pulsed electron-beam.
Isochronal annealing for 20 min was done over a temperature range from 300 to 1000°C. No drastic variation of sheet
carrier concentration, measured at the implanted surface,
could be observed even if thermal annealing temperature was
increased to 1000°C. This is believed to be due to the fact that
almost all P atoms implanted were electrically activated by the
electron-beam annealing and the carrier concentrations .did
not exceed the solid solubility limit for P in Si (1-5 x
1021/cm3).10 On the other hand, a slight improvement in carrier mobility was detected as increasing thermal annealing
above 500°C. To examine in more detail the annealing oehaviour, thermal annealing was carried out for 20 min at a fixed
temperature in a range from 400 to 1000°C. When thermal
anneal was carried out at a temperature between 500 and
700°C, an improvement on mobility was detected but no
appreciable change in carrier concentration profile could be
observed, as shown in Fig. 2. The results indicate that the
improvement can be attributed to the annihilation of crystal
defects still remaining and/or newly introduced by electronbeam annealing. At higher temperatures, some redistribution
of implanted P occurred, giving rise to a decrease in carrier
concentrations in deeper part of profile as seen in Fig. 2.
In summary, highly doped n-type Si layers have been formed
by P + implantation and a single shot of a pulsed electron
beam. Carrier concentrations are uniform over the profile, and
this feature can be maintained during additional thermal cycles
at temperatures below 700°C that will be encountered in a
device fabrication process. A slight improvement in mobility is
electron-beam-annealed layer will be applicable to the ohmic
contact region of Si devices.
T. SUGIYAMA
N. OKANO
Y. ISHIKAWA
College of Engineering
Hosei University
Kajino-cho, Koganei, Tokyo 184, Japan
4th December 1979
References
1 GREENWALD, A. C , KIRKPATRICK, A. R., LITTLE, R. G., a n d MINNUCCI,
j . A.: 'Pulsed-electron-beam annealing of ion-implantation
damage', J. Appl. Phys., 1979, 50, pp. 783-787
2 K AM INS, T. i., and ROSE, P. H.: 'Electron-beam annealing of ionimplantation damage in integrated-circuit devices', ibid., 1979, 50,
pp. 1308-1311
3 INADA, T., TOKUNAGA, K., and TAKA, s.: 'Pulsed electron-beam an-
nealing of selenium-implanted gallium arsenide', Appl. Phys. Lett.,
1979, 35, pp. 546-548
4 MCMAHON, R. A., and AHMED, H. : 'Electron-beam annealing of ion-
implanted silicon', Electron. Lett., 1979, 15, pp. 45-47
5 REGOLINI, J. L., SIGMON, T. w., and GIBBONS, J. F.: 'Metastable
75
As
concentrations formed by scanned cw e-beam annealing of
75
As-impIanted silicon', Appl. Phys. Lett., .1979, 35, pp. 114-116
Press, New Yoik, 1962)
7 GIBBONS, J. F., JOHNSON, w. J., and MYLROIE, s. w.: 'Projected range
statistics' (Dowden, Hutchinson and Ross, Stroudburg, Pa., 1975)
8 WHITE, c. w., NARAYAN, }., and YOUNG, R. T.: 'Laser annealing of
ion implanted silicon'. Proceedings of the laser-solid interactions
and laser processing symposium, Boston, Mass., Nov. 1978
9 INADA, T., KATO, s., MAEDA, Y., and TOKUNAGA, T. : 'Doping profiles
in Zn-implanted GaAs after laser annealing', J. Appl. Phys., 1979,
50, pp. 6000-6002
10 WOLF, H. F. (Ed.): 'Silicon semiconductor data' (Pergamon Press,
Oxford, 1969)
0013-5194/80/020054-02\$! .50/0
PROPERTIES OF A SIMPLE NOISESEQUENCE GENERATOR
Indexing terms: Binary sequences, Noise generators
A simple digital circuit, the sequentially masked m-sequence
generator, has been investigated as a source of noise. Analytical results are presented for the statistics of pulses (runs of 1)
and the principal experimental results are presented for the
statistics of gaps (runs of 0).
02
0 3 (K
depth, urn
05
06
f7iZ72l
Fig. 2 Effect of additional thermal annealing at 700 (A) and 1000°C (D)
on doping profiles for P+-implanted (5 x 10li cm'2) silicon samples
annealed previously by electron-beam irradiation at an energy density of
0-92 J/cm2: O sample annealed by electron-beam irradiation at 0-92
J/cm2 (without thermal anneal)
ELECTRONICS LETTERS
17th January 1980
Vol.16
Introduction: While involved in developing an adaptive communications system, the present authors found a requirement
for a generator of binary sequences that simulated the noise
characteristics of certain digital communication systems. Accordingly, the generator shown in Fig. 1 was investigated. It
had the merit of simplicity, and could be implemented easily
either in hardware or in software (for simulation studies). The
output of an m-sequence generator12 was complemented and
passed through an AND-gated shift register. The output of the
device will be called a 'sequentially masked m-sequence'; the
m-sequence was complemented before being sequentially
No. 2
55
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