Conductance Measurements of Thermally Annealed, Si-Implanted Quartz
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SI-IMPLANTED
QUARTZ Alex R. Hodges and Gary C. Farlow Physics Department, Wright State University, Dayton, OH
45435.
ABSTRACT Preliminary conductance measurements of Si implanted, a-Quartz which had been annealed in Ar to 1000 0 C have been made using a bridge method. The quartz was implanted to a dose expected to yield Si precipitates inside the quartz upon annealing. The measured conductivity, based on a geometry deduced from TRIM calculations and several trans-conductance measurements, is - 2 x 10-4 (Q m)-l. This is consistent with large islands of Si in series with an insulating matrix.
BACKGROUND AND SAMPLE PREPARATION It has been shown that when Si is implanted into quartz and subjected to rapid thermal annealing that crystalline islands or layers of precipitated Si will form at roughly the mean range of the 1 2 This process is the reverse of the SIMOX process implanted Si. now used in device fabrication.
In this paper we describe
preliminary measurements of the trans-conductance of such buried 'layers'
of Si.
In order to prepare suitable samples it is necessary to implant enough Si to form a layer super-saturated with Si in the vicinity of the mean range.
The criterion is
that the number density of
implanted Si plus the number density of native Si in SiO 2 exceeds the number density of Si atoms in elemental Silicon.
The required
number densities are listed in Table I. We chose 120 Kev for implantation since this is high enough to minimize sputtering and small enough to have a rather narrow implanted-ion distribution, thus minimizing the dose required. parameters of the implantation are listed in Table II.
Other
The Si ion
distribution from a TRIM-892 simulation of this implantation of Si into quartz gives an effective width of 100 nm. into a minimum required dose (flux) of 2.8 x 10 actual dose used was 4 x
This translates 17
Si/cm
2
.
017 Si/cm2 which corresponds to a
423 Mat. Res. Soc. Symp. Proc. Vol. 38801995 Materials Research Society
The
Table I.
showing the number
Table II.
densities of Si in the beginning and final materials and the net density needed to obtain the final result. Atomic density of SI (atoms/cc) 5.0 x 1022
Si SiO
2.2 x 1022 2
Implanted SI ions
showing the im-
plantation parameters for the Si-implanted quartz (m From TRIM SIMULATION)
2.8 x 1022
Energy
120 keV
Flux
4 x 10 27/cm 2
Fluence
2.0 pA/cm 2
Temperature of sample
30*C
Range
1550 nm
Straggling
50 nmm
Precipitation occurs during annealing.
This can be
accomplished by either rapid thermal annealing or ordinary thermal annealing in an oxygen-free ambient.
(Annealing in the presence of
oxygen will allow the implanted Si to oxidize.)
It
is important to
have a very slow temperature rate of change in the temperature range 550 to 600*C:
Quartz undergoes a structural phase transition at
-575 0 C and the two phases have very nearly the same free energy.
If
the temperature changes too fast, the quartz will become confused as to which phase it
should assume leaving a glassy matrix.
CO
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