ECE 541/ME 541 Microelectronic Fabrication Techniqueszyang/Teaching/20182019SpringECE... · ECE541/ME541 Microelectronic Fabrication Techniques Page 41 Surface Resistivity In a regular

ECE541/ME541 Microelectronic Fabrication Techniques Page 1

ECE 541/ME 541Microelectronic Fabrication Techniques

MW 4:00-5:15 pm

Metrology and Characterization

Zheng YangERF 3017, email: [email protected]


Ellipsometry

Ohmic contacts

I-V, C-V, Hall effect measurements

Material CharacterizationPL, Raman, XRD, XPS, SIMS, EDX, etc


Ellipsometry

Ohmic contacts




Ellipsometry


What is ellipsometry?

• Ellipsometry is an optical technique used for analysis and metrology

• Non contact, non destructive method• It determines the change in polarization state of

light reflected from a sample. • Typically used for characterizing thin films

(thickness, optical constants – complex refractive index) .

• It is a model-based technique


What is ellipsometry?

• Transparent films from a sub-nanometre up to several microns can be measured using ellipsometry.

• The surface upon which the film is measured can be a semiconductor, dielectric or metal.

• The film can be transparent or absorbing on a transparent or opaque substrate (need contrast)

• The measuring polarized light can range from the ultra violet to the infra-red.


By convention, the polarization of light is described by specifying the orientation of the wave's electric field at a point in space over one period of the oscillation. When light travels in free space, in most cases it propagates as a transverse wave—the polarization is perpendicular to the wave's direction of travel. In this case, the electric field may be oriented in a single direction (linear polarization), or it may rotate as the wave travels (circular or elliptical polarization).


Polarized and un-polarized lightMost sources of electromagnetic radiation contain a large number of atoms or molecules that emit light. The orientation of the electric fields produced by these emitters may not be correlated, in which case the light is said to be unpolarized. If there is partial correlation between the emitters, the light is partially polarized. If the polarization is consistent across the spectrum of the source, partially polarized light can be described as a superposition of a completely unpolarized component, and a completely polarized one. One may then describe the light in terms of the degree of polarization, and the parameters of the polarization ellipse



Crossed Polarizers


Crystal polarizers (II)[birefringence]

The 2 output beams are polarized (orthogonally).

isotropiccrystal(sodiumchloride)

anisotropiccrystal(calcite)most stable polymorph of calcium carbonate (CaCO3)





Ellipsometry

Ohmic contacts

















Ellipsometry

Ohmic contacts




Semiconductor device measurements setup

30


I-V test setup

• Probe station• Large working distance microscope• Movable stage and platform• Movable optics• Movable electrical contacts

• Semiconductor Device Analyzer (SDA)

31


Probe Station parts

32


Micropositioners

33


Probes

34


Tips

35

Metals used: Tungsten, Steel, Palladium, Osmium.


Complete setup

36


Semiconductor device analyzer

37


I-V characteristic curve of Diode


What is Four Point Probing

• Four Point Probing is a method for measuring the resistivity of a substance.


How the system works

• In order to measure the resistivity of a substance, four points of contact must be made with the probe and the substance.

• Current goes through the two outer probes, and the difference in voltage is measured between the two inner probes.

• Through this process the resistance can be calculated.


Surface ResistivityIn a regular three-dimensional conductor, the resistance can be written as

where ρ is the resistivity, A is the cross-sectional area and L is the length. The cross-sectional area can be split into the width W and the sheet thickness t.By grouping the resistivity with the thickness, the resistance can then be written as:

Rs is then the sheet resistance.


High-accuracy capacitance measurements

An AC signal of known frequency is applied through an internal low value resistor and the capacitor under test in a series configuration. The AC current flowing into the capacitor must also flow through the resistor, creating an AC voltage across the resistor.

The magnitude and phase of this voltage can be measured and compared to the original AC signal, and the capacitance can be computed. Techniques such as this frequency‐domain measurement can be very accurate.

LCR meter (Inductance (L), Capacitance (C), and Resistance (R))


Tools for measurement

Probe Station


Agilent Semiconductor Parameter Analyzer


Capacitance – Voltage Measurements

• capacitance voltage (C-V) testing is to determine semiconductor parameters, particularly in MOSCAP and MOSFET structures.

• C-V measurements are also widely used to characterize other types of semiconductor devices and technologies, including bipolar junction transistors, JFETs, III-V compound devices, photovoltaic cells, MEMS devices, organic thin film transistor (TFT) displays, photodiodes, and carbon nanotubes (CNTs).

Metal‐Oxide‐Silicon (MOS) capacitor


Capacitance – Voltage MeasurementsC‐V measurements can reveal oxide thickness, oxide charges, contamination from mobile ions, and interface trap density in wafer processes.

A deep depletion C–V curves for an SiO2/Si MOS capacitor. NA = 1017 cm−3, tox = 10 nm, A = 5 × 10−4 cm2.

The capacitance is determined by superimposing a small‐amplitude ac voltage v on the dc voltage V . The ac voltage frequency is typically 10 kHz to 1 MHz with 10 to 20 mV amplitude.



Basic Physical Phenomena of Hall Effect• When an electron moves in a direction perpendicular to an applied

magnetic field, it experiences a force (Lorentz force) acting normal to both directions and moves in response to this force (see below for an n-type semiconductor) – Constant current I (flows

along x‐axis) in the presence of magnetic field B (z‐axis) causes Lorentz force F (y‐axis)

– Causes electron paths to bend towards negative y‐axis

– Charge builds up on the surface of the side of sample, and the potential drop across the two sides of the sample is known as the Hall voltage (VH)

B V=0

V‐VH

xv

yB

F

z

Coordinate System

Lorentz Force F=‐ev x B

d

I e‐

References: 2, 3.


When electrons flow withoutmagnetic field...

t

d

semiconductor slice

+ _

I I


When the magnetic field is turned on ...

B-field

I qBv


As time goes by...

I

qE

qBv = qElow

potential

highpotential


Finally...

B-field

I

VH


Basic Hall effect measurement system

53


Ellipsometry

Ohmic contacts


Material CharacterizationPL, Raman, XRD, XPS, SIMS, EDX, etc(please also refer to Lecture 16, 17, and 25 for more details)


Photoluminescence Spectroscopy

A laser excites electrons from the valence band into the conduction band, creating electron-hole pairs

These electrons and holes recombine (annihilate) and emit a photon.

The number of emitted photons (intensity) as a function of energy, which is photoluminescence (PL).

CB

VB

Electronic bound state

hexcitation hemission

E

k

PL Intensity

Laser energy

Continuum states


Discovery of Raman Spectroscopy

Mr. Raman won the Nobel Prizeof Physics in 1930, “for his work on the scattering of light and for the discovery of the effect named after him”.

In 1928, Raman discovered that the spectrum of scattered lines of CCl4liquid not only consisted of the Rayleigh lines but a pattern of lines of shifted frequency ——the Raman spectrum.

C.V. Raman (1888-1970)


L L

q

S

S

S

S

q

Stokes

Anti-Stokes

qLS qLS

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ECE 541/ME 541 Microelectronic Fabrication Techniqueszyang/Teaching/20182019SpringECE... · ECE541/ME541 Microelectronic Fabrication Techniques Page 41 Surface Resistivity In a regular