Chemistry Reference
In-Depth Information
TABLE5.6.FinalResultsoftheFittingProcedureAppliedtoa
StratifiedStructureonaSiliconWafer
Element Composition (%)
Density (g/cm
3
)
Structure
Cr
Fe
Ni
Pd
Si
Thickness (nm)
Upper layer
46.7
29.5
23.8——5.9
7.0
Lower layer———100 — 257.0
11.2
Substrate————100
∞
2.3
Source
: Table from Ref. [3], reproduced with permission. Copyright1996, John Wiley and Sons.
rough estimate more sophisticated [175]. The relative standard deviation of the
individual data is about 1-2%.
Ultrashallow junction layers with boron and arsenic ions implanted in Si
wafers can serve as acceptors and donors, respectively. Such layers are
important for downsizing the components in the silicon ULSI technology.
The ions were implanted with energies of 0.2 to 3 keV in a depth of 3 to 20 nm
and a total dose or fluence of 1
×
10
14
to 5
×
10
15
ions/cm
2
. Hönicke
etal
. [185]
determined the boron and arsenic concentrations as a function of depth.
GI-XRF was carried out with synchrotron radiation at BESSY II using low-
excitation energy, a UHV chamber, and a windowless SDD. Relevant concen-
tration/depth profiles could also be calculated
abinitio
with a reference-free
fundamental parameter method. The total implanted fluence or dose was
determined by integration of these profiles. Deviations from the nominal
dose were below 10%. In contrast to GI-XRF, the well-established and
approved method SIMS (secondary ion mass spectrometry) showed differing
profiles that were shifted toward the surface. Such significant deviations are
caused by matrix and transient effects, especially for low-energy implantations
and the near-surface region. The profiles calculated by the theoretical TRIM
program (Transport and Range of Ions in Matter) fit even much better.
Silicon dioxide has been used as a gate oxide material in the last decades.
The thickness of such dielectric layers could be permanently reduced; however,
below 2 nm the leakage current due to tunneling increased and the reliability
suffered severely. For that reason, the silica gate was replaced by a material
with a high dielectric constant (
k
value
>
3.9). Hafnium or zirconium can be
implanted as a shallow layer of some nanometer thickness in a silicon wafer
showing a double capacity but much smaller leakage current (0.01-fold in
comparison to a thin silica layer). Ingerle
etal
. investigated shallow implanted
layers of arsenic in silicon and additionally of Hf-based high-k layers with 2 and
5 nm thickness, called ultrashallow junctions (USJ). GI-XRF was shown to be a
powerful technique for the determination of the composition of the different
layers and the whole implantation dose or fluence [186,187]. XRR was applied
to get additional information on the thickness of mono- and multilayers,
directly
and
nondestructively.
A
software
package
was
developed
for
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