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SEMI M34-0299 © SEMI 1999 7 Table 1. Specification Summary Parameter Reference Example Values Method Wafer diameter (D) ASTM 613 150 mm, 200 mm Optical comparitor Wafer thickness ASTM 533 Thickness gauge Thickness variat…

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SEMI M34-0299 © SEMI 1999 6
7.4.4 Surface Roughness — Surface roughness is a
measure of the microscopic topology of the wafer
surface. The effect of this parameter may be in Gate
Oxide Integrity (GOI) on MOS devices, depending on
the design and process. The measurement of surface
roughness is done on an atomic scale by an Atomic
Force Microscope (AFM). With AFM, it is suggested
that four measurement areas of greater than 2 µm
2
be
measured at each of five measurement locations, with
the measurement locations distributed as in Figure 1.
Because of the expense of this measurement, a
sampling plan should be established with the supplier.
7.4.4.1 Standards for specification of surface rough-
ness are being developed for bulk silicon and shall be
applicable here when adopted.
7.4.5 HF Defect Measurements - Test Methods
Measurement of the microscopic etch pit density
following an HF etch is a method commonly used to
disclose defects in SOI material. Pitting of the top
silicon surface may be present before the HF etch or be
caused by HF etching. For this destructive
measurement, at least one quarter of a wafer should be
used and preferably a whole wafer. The sample is
placed in concentrated (49%) HF for 10 to 15 minutes,
then removed, rinsed and dried. If there are pits in the
SI surface, metal particles embedded in the surface or
silicides formed in the top Si layer, the HF will etch the
metals/silicides and then etch the buried oxide. This
results in a section of the buried oxide being etched out
that is 25−50 µm diameter (depending on the etch time)
centered on the original pit or particle. The defect
density is then measured in an optical microscope using
a 5X objective and 10X eyepiece or comparable setup.
The sample should be scanned 2−3 times near the
center of the wafer if a whole wafer is used to get
sufficient statistics. If a piece of a wafer is used, the
scan should be adjusted accordingly. The total area
scanned should be at least 10 cm
2
. Care should be taken
to exclude edge density depending on the expected
impact on yield versus material cost. A typical
specification is that the HF defect density should be less
than 1/cm
2
.
SEMI M34-0299 © SEMI 1999 7
Table 1. Specification Summary
Parameter Reference Example Values Method
Wafer diameter (D) ASTM 613 150 mm, 200 mm Optical comparitor
Wafer thickness ASTM 533 Thickness gauge
Thickness variation ASTM 533
< 3 µm
Thickness gauge
Wafer warp ASTM F 657, F 1390
≤ 30 µm for D = 150 mm
Jig + gauge
Crystal orientation ASTM 26 X-ray diffraction
a) front surface
(100) ± 1°
b) back surface
Substrate type/dopant ASTM 42 Hot point probe
Substrate resistivity ASTM 84 4-point probe
Substrate RRG ASTM 84 4-point probe
Surface Si thickness Section 7.1.5 50 nm to 500 nm SE/optical reflectance
Surface Si uniformity Section 7.1.3
± 5 nm
SE/optical reflectance
Buried oxide thickness Section 7.1.6 50 nm to 500 nm SE/optical reflectance
Buried OX uniformity Section 7.1.3
± 10 nm
SE/optical reflectance
Crystal defect (EPD) Section 7.2 < 10 E7/cm
2
SEM examination
Secco etch
Buried OX pinholes < 0.1/cm
2
a) CuSO
4
plating
b) BOX capacitor @ 1 nA
Metal contamination Section 7.4.1 total < 10
11
atoms /cm
2
TXRF
a) per unit area
b) per unit volume
Particles Section 7.4.2
≤ 20 (> 0.25 µm) / wafer
Automated particle counter
Haze Section 7.4.3 See Table 2. Visual inspection
Slip ASTM F 523* See Table 2. Visual inspection
Scratches ASTM F 523* None Visual inspection
Chips ASTM F 523* See Table 2. Visual inspection
Surf Spot Discolor ASTM F 523 See Table 2. Visual inspection
Foreign matter ASTM F 523 See Table 2. Visual inspection
Backside contamination ASTM F 523 Visual inspection
Surface roughness Section 7.4.4 5 Atomic force microscope
(AFM)
Inclusions Section 7.4.5
* The user and supplier may agree on an edge exclusion for these specifications. For example, the area within 6 mm proximity of
the wafer edge may be excluded.
SEMI M34-0299 © SEMI 1999 8
Table 2. Example SIMOX Wafer Surface Inspection Criteria
Criterion Allow Quantity Description
Slip 0.3 mm: NONE
0.1−0.3 mm: < 15 mm total
< 0.1 mm: OVERLOOK
6 mm edge exclusion
Scratch NONE 6 mm edge exclusion
Contamination NONE Backside
Stain < 5 spots < 0.05 cm
2
total area
Edge Chips/Cracks < 1.5 mm circumferential < 1.8 mm radial
combined length 1 × bright light
Pits and Dimples < 0.5 mm - 10/wafer
> 0.5 mm - NONE
1 × bright light
Haze Moderate haze - NONE
Heavy haze - NONE
Non-uniform haze - NONE
Light uniform haze is acceptable.
(Iterate between user and vendor.)
Foreign Matter (embedded particles) < 0.05/cm
2
< 3 embedded particles per 150 mm wafer
Table 3. SIMOX Electrical Parameters
Parameters Reference Value Method
Photoconductivity Lifetime
(Backside)
Section 8.1
> 1 msec.
microwave
Photoconductivity Lifetime
(Front side)
Section 8.1 TBD microwave
BOX Breakdown Section 8.2 > 5 MV/cm I-V
BOX Pinholes Section 8.3 < 0.2 cm
2
I-V
BOX Charge Section 8.4 < C-V
BOX Surface States Section 8.5
< 5 × 10
10
/cm
2
C-V
Doping Density
Sub, Surface
Section 8.6 TBD 4-point probe
8. Electrical Parameters
8.1 Photoconductivity Lifetime — This is measured by
creating an excess of carriers (typically by using a light
source) and measuring the slope of the decay curve.
Several pieces of commercial equipment are available
for this purpose. This requires that polysilicon is not
deposited on the backside, as is sometimes done for
gettering. Also, surface passivation may be needed for
lifetime measurements. Backside measurements
indicate the quality of the substrate and can be
performed by traditional methods. Frontside
measurements are more difficult and must be performed
using incident light which can be entirely absorbed
before reaching the underlying substrate.
8.1.1 Typically, the sample is placed on a micro-wave
wave guide post, forming part of a transmission line
circuit. The microwave reflection is determined by the
total conductivity of the sample and the conductivity is
modulated by an intense light pulse. When the light is
turned off, the microwave detects an exponential decay
in conductivity from which a decay constant is
determined. The photoconductivity lifetime is a result
of the recombination velocity at the surfaces, volume
recombination in the silicon layer, and any trapping.
Measurements are made independently on the front and