Chapter 1.6
I - Substrate Specifications
Polished Single-Crystal Silicon, Prime Wafers
(all numbers nominal)
Wafer Specification Table
|
Diameter |
100 mm |
4-inch |
150 mm |
6-inch |
|
Thickness |
525 µm |
20.5 mils |
675 µm |
26.3 mils |
|
Primary Flat Length |
32.5 mm |
|
57.5 mm |
|
|
Secondary Flat Length |
18.0 mm |
|
37.5 mm |
|
|
Bow, max |
40 µm |
|
60 µm |
|
|
Wrap, max |
40 µm |
|
60 µm |
|
|
Total thickness variation (max. Flatness) |
10 µm |
|
10 µm |
|
II - Sorting Unlabeled Wafers
The quality, resistivity type, bulk
resistivity, and crystal orientation of unidentified Si wafers can be
determined if the wafers are new (unused). The following is a description of the
procedures to follow for identifying "unknown" wafers.
1.
Bright Light
Inspection
(1) Inspect
all wafers under the bright light in V1 (VLSI area).
(2) Discard
any badly scratched or very hazy wafers.
2.
Determining
Resistivity Type
Use the Tencor tentype tool (kept in the drawer under the Nanospec
/ CV 4-point probe drawer, under the
(1) Place
the wafer, unpolished (dull) side down, over the probe opening.
(2) Depress
the button (don't touch the wafer with fingers, tweezers, or vacuum wand while
testing).
(3) N
or P for dopant type will be displayed.
3. Measuring
Bulk Resistivity
Use VEECO FPP 4-POINT PROBE: Please see the instruction posted in Chapter 8.01 and the SLICE option of
the tool with proper wafer thickness to be entered under the PRGM mod.
http://microlab.berkeley.edu/labmanual/chap8/8.01.html
4.
Determine
Using a diamond scribe and tweezers, cleave one wafer from each box.
This is a destructive method.
(1) With
a diamond scribe, make a small nick in the wafer at the major flat.
(2) Apply
pressure to the nicked area with tweezers in order to cleave the wafer.
(3) Make
another nick in the cleaved piece and repeat step 2.
(4) If
the cleaved pieces form rectangles (cleave at 90 deg. angles), then the crystal
orientation of the Si is <100>. If the cleaved pieces form triangles
(cleave diagonally), then the crystal orientation of the Si is <111>.
(5) Alternately,
flat and secondary flat orientation may be compared to orientation conventions
shown in the Semiconductor Technology Handbook.
III - P-Type 4-inch Wafer Roughness Data
These are AFM images of P-type 4" prime wafers (below). These wafers are very smooth with the RMS roughness of around 2-4 angstroms. For each sample there are two 5 x 5 micron images, one entitled roughness analysis and the other entitled flatten. The samples were cut from 4" p-type prime wafers, and diced by disco saw utilizing a 2-micron sacrificial photoresist layer. After the dicing, samples were washed in acetone, IPA and DI water, then atomic forced microscope (AFM) was used to measure the roughness.
