Transcript Jialin_Zhao_Shallow_Junction

Measuring ultra-shallow junction
Jialin Zhao
Resistivity and Sheet resistance
• IRS roadmap 2003: 10 nm junction with sheet
resistance 500 Ω/sq
• Electrical resistivity
• Sheet resistance
when L= W
Four point probe measurement I
• The most common method of measuring the
wafer resistivity is with the four-point probe.
• Measuring the current that flows for a given
applied voltage. Using four probes instead of
two allows us to force the current through the
two outer probes, where there will still be contact
resistance and current spreading problems, but
we measure the voltage drop with the two inner
probes using a high-impedance voltmeter.
Problems with probe contacts are thus
eliminated in the voltage measurement since no
current flows through these contacts.
Four point probe measurement II
Constant current source
R
I
V
Voltmeter
Wafer
Hall Effect Measurements
•The Hall effect was discovered more than 100 years ago
when Hall observed a transverse voltage across a conductor
subjected to a magnetic field.
•The technique is more powerful than the sheet resistance
method described above because it can determine the
material type, carrier concentration and carrier mobility
separately. The basic method is illustrated in the next slide.
The left part of the figure defines the reference directions and
the various currents, fields and voltages; the right part of the
figure illustrates a top view of a practical geometry that is often
used in semiconductor applications.
Conceptual representation of Hall effect
measurement.
The right sketch is a top view of a more practical implementation.
RH 
Ey
JxB
V y W  TV y



IB WT
IB
Spreading Resistance Probe
SRP Probing
Probing
Problem:
Clear bevel edge to distinguish different layers;
Bevel angle; step increment; probe tip; calibration;
Probe penetration
Probes will penetrate ultra-shallow junctions
T. Clarysse et. al “Impact of probe penetration on the electrical characterization
of sub-50 nm profiles”,J. Vac. Sci. Technol. B, Vol. 20, No. 1, Jan/Feb 2002
Error due to probe penetration
T. Clarysse et. al “Impact of probe penetration on the electrical characterization
of sub-50 nm profiles”,J. Vac. Sci. Technol. B, Vol. 20, No. 1, Jan/Feb 2002
Secondary Ion Mass Spectrometry
(SIMS)
Bombardment of a sample
surface witha primary ion
beam followed by mass
spectrometry
of
the
emitted secondary ions
constitutes secondary ion
mass spectrometry (SIMS).
.
Uses
• NASA first developed SIMS in the 1960s to
investigate the composition of Moon rocks.
• SIMS can be used to determine the composition
of organic and inorganic solids. This can
generate spatial or depth profiles of elemental or
molecular concentrations.
• These profiles can be used to generate element
specific images of the sample that display the
varying concentrations over the area of the
sample
Basic Overview
http://www.u.arizona.edu/~xiuminj/web/SIMSdefault.htm
Secondary ion generation
• The sample is prepared
in an ultra high vacuum.
• A beam of primary ions
or neutral particles
impacts the surface with
energies of 3-20 keV.
• A primary ion or particle causes a collision
cascade amongst surface atoms and between .1
and 10 atoms are usually ejected. This process is
termed sputtering. Secondary ions are mass
analyzed and counted.
Silicon doping analysis
• To produce a high ion yield and a small mass
interference, Cs+ is normally chosen for n-type
dopants (As, P, Sb), while O2+ is chosen for p-type
dopants (B, In)
• Monitoring the secondary ion count rate of selected
elements as a function of time leads to depth profiles.
• To convert the time axis into depth, the SIMS analyst
uses a profilometer to measure the sputter crater
depth. A profilometer is a separate instrument that
determines depth by dragging a stylus across the
crater and noting vertical deflections. Total crater
depth divided by total sputter time provides the
average sputter rate
SIMS of ultrashallow junctions
W.Boyd, et al. “Consideration of in-lin qualification for ultrashallow junction implantation,”.
J. Vac. Sci. Technol. B, Vol. 16, No. 1, Jan/Feb 1998
Problems
• Chemical concentration
• Steady state in the first 5-10 nm
• Surface clean, primary ions conditions
• The limiting may be 2keV implantation
• Not an in-line process
Thermal wave method I
• Thermal Wave is
the pre-eminent
technology for
measuring the
characteristics of
wafer implants,
whichh is
developed and
patented by
Therma-Wave Inc
www.thermalwave.com
Thermal Wave Method II
•Thermal waves are generated by an
intensity modulated laser beam, so called
"pump laser“. For semiconductor materials,
excessive electron-hole free carriers
"plasma waves" produced by the pump
laser are also present.
•The optical properties of most materials,
such as refractive index, are dependent to
some extent on sample temperature.
•These variations in reflectivity can be
detected by measuring the modulated
reflectance of an optical probe beam, so
called "probe beam", which is reflected
from the sample surface.
•Effects of thermal and plasma waves to optical
parameters such as silicon reflectivity for
intrinsic and heavily-doped silicon are different
Thermal Wave method III
• TRIM
simulation.
The
maximum penetration depth for
ion concentration is defined as
the 1018 ion concentration level.
The mechanical damage was
calculated from the damage
produced by ions and recoils
~interstitials and vacancies! as
simulated with TRIM and the
maximum penetration depth is
defined as the 10-4 level of
damage.
• Damages could be directly
correlated to ion concentration
L. Nicolaides, et. al. “Study of low energy implants for ultrashallow junctions using
thermal wave and optical techniques,” Rev. Sci. Instrum., Vol. 74, No. 1, January 2003
Thermal Wave method IV
• TW signal has linear
relation with implant
energy under 2keV.
L. Nicolaides, et. al. “Study of low energy implants for ultrashallow junctions using
thermal wave and optical techniques,” Rev. Sci. Instrum., Vol. 74, No. 1, January 2003
Two dimension doping profile I
• TEM: selective etching: HF+HNO3+CH3COOH
C.Spinella et. Al. “Two-dimensional junction profiling by selective chemical etching:
applications to electron device characterization,“J. Vac. Sci. Technol. B 14(1), Jan/Feb
1996 414-420
G. Fortunato et al. “Ultra-shallow junction formation by excimer laser annealing and low
energy ( less than or equal 1 keV) B implantation: A two-dimensional analysis, “ Nucl.
Instr. and Meth. in Phys. Res. B 186 (2002) 401–408
Two dimension doping profile II
• Electron Holography
• The electrostatic potential
distribution across a p-n
junction induces a local
phase shift in the plane
electron wave pass
through the sample
• Electron biprism is used
to measure the amplitude
and phase of the
wavefront.
W.D. Rau, et. al IEDM 1997 pp713
Two dimension doping profile II
W.D. Rau, et. al. “Two-Dimensional Mapping of the Electrostatic Potential in
Transistors by Electron Holography,” Phys. Rev. Lett. 82 , no 12, MARCH 1999