Wafers always come doped, at least 1013 cm-3 from naturally occurring impurities. Semiconductor doping is always < 1
at%, i.e., < 5 x 1020 cm-3 (5×1022 Si atoms/cm3) Implantation dose is given in ions/cm2. To calculate doping
concentration, you need to know the depth of implanted region (50-500 nm typical) Implantation doses typical 10131015 ions/cm2 ( 1018 – 1020 cm-3 for shallow implants)
Dopant level
Notation
Concentration
Resistivity
lightly doped
moderately doped
highly doped
very highly doped
n- , pn, p
n+, p+
n++, p++
1013-1015 cm-3
1015-1018 cm-3
1018-1020 cm-3
~1020
cm-3
>10 Ohm-cm
10-0.1 Ohm-cm
0.1-0.001 Ohm-cm
0.001 Ohm-cm
Material Wet etchant
<Si>
KOH
SiO2
HF
Al
H3PO4
W
H2O2
Au, Pt aqua regia
Cu
HCl
Mask material
oxide, nitride
resist
resist
resist
resist
resist
Also etches
Al
Al
Notes
anisotropic
isotropic
isotropic
isotropic
isotropic
isotropic
Material
Silicon/poly
SiO2
Si3N4
Al
W, Mo, Ti
Pt
Au, Cu, Ni
Plasma etchant
SF6, Cl2
CHF3, C4F8
SF6
Cl2, BCl3
SF6
none
none
metals
not Ni, Au
Also etches
nitride, W, Ti
nitride
Si, W, Mo, Ti
Si
Si, nitride
Notes
If deep  hard mask
lift-off option
damascene, plating
Metal deposition methods
Al: sputtering, evaporation
W: sputtering (for planar), CVD for 3D structures
Ti, TiW: sputtering
Cr: sputtering
Au: sputtering, evaporation, electroplating
Pt: sputtering, evaporation
Cu: sputtering, evaporation, electroplating, CVD
Structural film
polysilicon
silicon nitride
oxide, metal
nickel
aluminum
gold
copper
parylene
SU-8
Sacrificial film(s)
CVD oxide
oxide; Al
silicon
Cu; resist
resist
Cu; resist
resist
resist
Cu; Al
Sacrificial etch(es)
HF, liquid or vapor
HF; NaOH, H3PO4
XeF2, SF6 plasma
HCl; oxygen plasma
oxygen plasma
HCl; oxygen plasma
oygen plasma
acetone, other solvents
HCl; NaOH, H3PO4
Thermal limits: Front end: 900-1200oC; Intermediate range: 450-900oC: no metals on the wafer; metalcompatible temperatures up to 450oC; Resist compatible range, < 150oC
Single sided vs. double sided processing: Liquids and gases all around wafers vs. beams of photons, ions, atoms
hitting wafer
Thermal or CVD oxide ?
Thermal diffusion or ion implantation?