Process of silicon wafer manufacturing from sand to wafer, with some comparisons and applications

1. Yuvraj Chaudhary

2. 
 Silicon
 Fourteenth element
 Group IV A element
 Dark gray solid
 Melting point of 2570° F (1410° C)
 Boiling point of 4271° F (2355° C) d
 Density of 2.33 g/cm3
 Sand is composed of silica (SiO2), and is the starting point for making a
wafer. This case study talks about how it is processed from sand to
manufacture wafers.
 When silicon is purified and doped with elements such as boron,
phosphorus and arsenic, it is used as a semiconductor in various a
applications.
INTRODUCTION

3. 
The whole methodology has been divided into four
steps for the sake of simplicity and make reasonable
comparisons in between old-modern techniques and
according techniques as per need:
 Converting sand to silicon
 Creating a cylindrical crystal
 Works Before Slicing
 Slicing the crystal into wafers
METHODOLOGY

4. 
CONVERTING SAND TO SILICON
 Silica(Sand) is reduced(O2 is
removed from it)
Silica and Carbon is heated in an
electric arc furnace to a temperature
in excess of 2,000°C.
 SiO2 reacts with excess C to first form SiC.
At high temperature, the SiC reduces SiO2
to form Si
SiC (s) + SiO2 (s) Si (l) + SiO (g) + CO (g)
 The Si(l) is removed from the bottom of the furnace. The main metallic
impurities are Al and Fe in ppm level. Further purification is needed to
make electronic grade silicon (EGS) and impurity concentration is reduced
to ppb levels.

5. 
CONVERTING SAND TO SILICON
(contd.)
 Reactions Involved are:
Si (s) + 3HCl (g) SiHCl3 (g) + H2 (g)
2SiHCl3 (g) + 2H2 (g) 2Si (s) + 6HCl (g)
 Impurities such as iron, aluminum, boron and phosphorous also react to give their
chlorides, which are then removed by fractional distillation.

6. 
CREATING A CYLINDRICAL
CRYSTAL
 Czochralski technique (Cz)
 Electronic-grade silicon melted above 1414°C
 Crucible made of SiO2/SiNx(to minimize contamination)
 Process:
A tiny crystal of silicon is then dipped into the molten
silicon and slowly withdrawn while being continuously
rotated in the opposite direction to the rotation of the
crucible. The crystal acts as a seed, causing silicon from
the crucible to crystallize around it. The seed crystal is
also rotated while it is being pulled, to ensure uniformity
across the surface. This builds up a rod called a boule
that comprises a single silicon crystal
Raw electronic-grade silicon has a polycrystalline(defects called grain boundaries
between silicon crystals) structure. These anomalies affect local electronic behavior,
polycrystalline silicon is unsuitable for semiconductor manufacturing.

7. Animation- Czochralski Technique

8. 
CREATING A CYLINDRICAL
CRYSTAL
(Contd.)
 Float Zone technique (Fz)
 Suited for small wafer production, with low
oxygen impurity
 Process:
The float zone technique is suited for small wafer production,
with low oxygen impurity. A polycrystalline EGS rod is fused
with the single crystal seed of desired orientation. This is taken
in an inert gas furnace and then melted along the length of the
rod by a traveling radio frequency (RF) coil. The RF coil starts
from the fused region, containing the seed, and travels up. When
the molten region solidifies, it has the same orientation as the seed.
The furnace is filled with an inert gas like argon to reduce gaseous
impurities.

9. Animation- Float Zone Technique

10.  Monocrystalline silicon ingot
 Further improvements in machining efficiency and accuracy
 Checking of resistivity (Four-point probe technique)
 Confirmation of the dopant concentration
 Orientation is measured by x-ray diffraction
 After all, one or more flats are ground along the length of the ingot
 Flats, Two types:
 Primary flat - this is ground relative to a
specific crystal direction. This acts as a
visual reference to the orientation of the wafer.
 Secondary flat - this used for identification
of the wafer, dopant type and orientation.
WORKS BEFORE SLICING

11.  Inner Diameter Slicing
 Slicing done using diamond cutter
 Chemical etching of wafers(removal of contaminated or
damaged region, done in acid bath)
 Then, the surfaces are polished(first-rough abrasive
polish, followed by a chemical mechanical polishing
ab.CMP)
 Single side or both side polishing
SLICING CRSTALS INTO WAFERS
 Multi Wire Saw Slicing
 Effective over Wire EDM (Expected to be used in future)
 thin piano wires are fed to the ingot with slurry consisting of
abrasives and cutting oil
 small kerf loss and ability of cutting large-scale wafers and
multi wafers at the same time
 surfaces are polished using an abrasive slurry
 wafer is then etched in a mixture of nitric, hydrofluoric
and acetic acids

12. 
 Production and deep processing of diodes, rectifier
devices, circuits, and solar cell products.
 Integrated Circuit (IC)
 Computers, mobile devices/smart phones, tire
pressure sensor system
USES