Lexicon
B
BOW –
The deviation of the center point of the median surface of a free, unclamped wafer from a
median-surface reference plane established by three points equally spaced on a circle with
diameter a specified amount less than the nominal diameter of the wafer.
C
Carrier concentration
In contrast to metallic conductors such as aluminum copper, semiconductors have two
independent charge carriers: electrons and holes. The behavior of diodes, transistors, and
other semiconductor devices often hinges upon the relative concentrations of holes
(p) and electrons (n), expressed in cm3. In pure silicon, they are thermally generated in pairs. In this intrinsic state,
n and p remain equal. Their product is
np = n2 ≈
10E10/cm3 at room temperature. In a p-type substrate,
however, the substitution of acceptor atoms (like boron) into the silicon lattice results in
an excess of holes. Then pp>>np indicating an excess of majority-carrier holes over
minority-carrier electrons. The product
np = ni2
will remain constant under thermal equilibrium (no applied bias or other perturbations).
Conductivity Type
An n-type (negative-type) extrinsic silicon semiconductor is a semiconducting material that was produced by doping silicon with an n-type element of Group V A, such as P, As, or Sb. Consequently, electrons are the majority charge carriers of the material.
A p-type (positive-type) extrinsic silicon semiconductor is a semiconducting material that was produced by doping silicon with an p-type element of group III A, such as B, Al, or Ga. Since the dopants are acceptor atoms, holes are the majority charge carriers of the material.
An n-type (negative-type) extrinsic silicon semiconductor is a semiconducting material that was produced by doping silicon with an n-type element of Group V A, such as P, As, or Sb. Consequently, electrons are the majority charge carriers of the material.
A p-type (positive-type) extrinsic silicon semiconductor is a semiconducting material that was produced by doping silicon with an p-type element of group III A, such as B, Al, or Ga. Since the dopants are acceptor atoms, holes are the majority charge carriers of the material.
E
EPD –
Etch pits density.
F
FM – Flatness Measurements –
Describe the deviation of the front wafer surface, expressed in TIR or maximum FPD, relative
to specified reference plane when the back surface of the wafer is ideally flat, as when
pulled down by a vacuum onto ideally clean flat chuck. (ADE, Massachusetts)
Focal plane –
The plane perpendicular to the optical axis of an imaging system which contains the focal
point on the imaging system. (Massachusetts)
FPD – Focal Plane Deviation
The distance parallel to the optical axis from a point on the wafer surface to the focal plane of the optical system. (Massachusetts)
The greatest positive or negative deviation from a reference plane which approximates the focal plane, when the wafer is mounted on a flat vacuum chuck. (ADE)
The focal plane deviation is the greatest distance above or below the chosen focal plane. (Motorola)
The distance parallel to the optical axis from a point on the wafer surface to the focal plane of the optical system. (Massachusetts)
The greatest positive or negative deviation from a reference plane which approximates the focal plane, when the wafer is mounted on a flat vacuum chuck. (ADE)
The focal plane deviation is the greatest distance above or below the chosen focal plane. (Motorola)
G
GTIR – Global Total Indicated Reading –
Maximum peak to valley deviation of a wafer from a given reference plane.
GTIR = A + B
H
Hard Back Side Damage (HBSD) –
Is a technique of improving properties of Si wafers by bombarding the back sides of the
wafers with a wet stream of tiny quartz beads and extra clean wafers after that. HBSD is
applied very early in the production process of Si wafers. The back-side, physically damaged
layer, is removed later, in subsequent operations. In the HBSD result the damaged areas act
as the impurities (remnants from CZ crystal growth process) attractors and denude zones are
created in the material bulk, improving purity of the silicon (front-side especially). The
technique is applied by all the best wafers producers. We think that all heavily doped
wafers, made by the best world producers, undergo HBSD or similar techniques, like for
example brushing. Simply certificates are silent about that. The damage is not visible to
the human eye and special techniques of Si bulk analysis are necessary to detect that wafer
passed HBSD. We are sure to recommend HBSD material for any application.
Haze Free –
A silicon wafer having the best possible surface finish and micro-roughness on the order of
less than 10A.
L
Local Thickness Variation –
The local thickness variation to each point is the vector sum the elevation difference of
pairs of immediately adjacent points, expressed in micrometers per millimeter.
(Motorola)
LPD –
Light Point Defects.
N
Non-Linear Thickness Variation –
Describe the thickness variation on a wafer defined by a center thickness value and four
edge thickness values obtained ⅛″ from the edge of the wafer. (Guidici)
O
Orientation –
The growth plane of the crystalline silicon. Orientations are described using Miller Indices
such as (100), (111), (110), etc. Different growth planes and
orientations have different arrangements of the atoms or lattice as viewed from a particular
angle.
P
Peak to Valley flatness (P/V) –
The sum of the greatest positive & negative deviations for a reference plane which
approximates the median wafer surface plane when the wafer is mounted on a flat vacuum
chuck. (ADE)
Prime Grade –
The highest grade of a silicon wafer. SEMI indicates the bulk, surface, and physical
properties required to label silicon wafers as "Prime Wafers".
Primary flat –
The flat of longest length located in the circumference of the wafer. The primary flat has a
specific crystal orientation relative to the wafer surface; major flat.
Q
Quality Area –
The portion of a wafer within the specified parameter is determined. (ASTM)
R
Reclaim Grade –
A lower quality wafer that has been used in manufacturing and then reclaimed, etched or
polished, and then used a second time in manufacturing.
Resistivity –
The resistance that a unit volume of a material offers to the passage of electricity, the
electric current being perpendicular to two parallel faces. More generally, the volume
resistivity is the ratio of the potential gradient parallel with the current in the material
to the current density.
S
Secondary Flat –
Indicates the crystal orientation and doping of the wafer.
SEMI –
SEMI Organisation (https://www.semi.org/) is the global industry association representing the electronics manufacturing and design
industry, connecting more than 2,500 members and 1.3 million professionals worldwide (data
for March, 2023). SEMI members are responsible for the innovations in materials, design,
equipment, software, devices, and services that enable smarter, faster, more powerful, and
more affordable electronic products. Since 1970, SEMI has built connections that have helped
its members prosper, create new markets, and address common industry challenges.
Slice Orientation –
The crystallographic orientation of the surface of a wafer. The primary and most common
slice orientations are (100), (111) and (110).
Striations (dopant rings) –
SEMI standard says that striations are “helical features of Si wafer are ascribed to
periodic dopant incorporation differences occurring at the rotating solid-liquid interface
during crystal growth.” They are visible to the unaided eye after preferential etching. From
the experience I know that skilled and trained operators can see them without any etching on
some heavily doped wafers. The striations are not a wafer defect, but a residual feature
originating from dopant distribution during the crystal growth process. They do not affect
electronic properties of the wafers. For many years it was believed that growing ingots in
the outer space, with no gravity, prevents forming the striations. However NASA experiments
(NP-119 Science in Orbit: The Shuttle & Spacelab Experience, 1981-1986) tells us that “the
space-grown crystals had the same marked dopant striations seen in Earth-grown crystals,
confirming that Marangoni convection (flow driven by surface tension) may be a dominant
cause of the defects on Earth and in space.”
Striations
T
Taper –
Taper is the lack of parallelism between the back surface of the wafer and the selected
focal plane. The numeric value provided as a sort criterion is the maximum difference
between these two planes, not the slope of the surface, and is thus reported in micrometers
over the diameter not microns per millimeter. (Motorola)
Test Grade –
A virgin silicon wafer of lower quality than Prime, and used primarily for testing
processes. SEMI indicates the bulk, surface, and physical properties required to label
silicon wafers as "Test Wafers".
Thickness –
The normal distance through a slice or wafer in a direction normal to the surface at a given
point.
TIR ≡ PV
Difference in elevation between the highest and lowest points on the surface of a wafer and the value is presented as a magnitude. (Guidici)
The smallest perpendicular distance between two planes, both parallel with the reference plane, which enclose all points on the front surface of a wafer within the flatness quality area or the site, depending on which is specified. (ADE)
Difference in elevation between the highest and lowest points on the surface of a wafer and the value is presented as a magnitude. (Guidici)
The smallest perpendicular distance between two planes, both parallel with the reference plane, which enclose all points on the front surface of a wafer within the flatness quality area or the site, depending on which is specified. (ADE)
TTV – Total Thickness Variation –
Absolute difference in thickness between the thickest and thinnest parts of wafer.
TTV = A - B
W
Warp –
Difference between maximum and minimum deviations of the median surface relative to the
3-point backside reference plane or the best-fit median surface reference plane.