|
|
|
|
|
|
|
|
|
|
|
|
| PBS
1000 |
|
|
|
| Examples
of PBS™ Measurements |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
The maps on this page
and the following pages show PBS™ measurements on various silicon
wafers with differing types of defects, or none at all. In some cases
the V-MAP (scatter versus angle of the plane of incidence) is included
with the area maps if it shows a distinctive feature, otherwise it is
not included.
The maps below show
a V-MAP (left image) and an area map (center image) for a very high quality
defect free, 200mm wafer.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
 |
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Wafer
TEST070 (right image) is an example of a wafer with significant staining.
This type of feature is the result of the wafer not sitting flat against
the polishing pad, a situation usually caused by debris under the wafer. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Wafer
TEST206 has a map with a circular high scatter area in the center. This
was caused by the method used to position the wafer in the wax before polishing.
As in the case of TEST070, this wafer did not sit flat against the pad during
the polishing process. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Wafer
TESTG032 is another example of the wafer not sitting flat against the pad.
In this case, the center was slightly concave.
Wafer TEST80 is an
example of an Epi-wafer that is poor in quality. The red spots at the
top of the wafer map (right image) are particles that can be ignored.
The main problem is the high scatter level and the circular red area in
the center of the map. Typical Epiwafers have a higher scatter level than
polished wafers, but are completely uniform. The V-MAP (left image) for
this wafer is typical of an Epi-wafer V-MAP showing only one direction,
either O or 90 degrees.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
 |
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| The
process of making an Epi-wafer can cause serious problems if there is subsurface
damage in the substrate. Wafer TESTG23 shows the result of exposure to hydrogen
at high temperature. The V-MAP shows a single strong direction at about
40 degrees. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| The
area map shows obvious polishing damage near the center of the wafer. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| The
high-resolution area map was made close to the center of the wafer and shows
the damage more clearly. The isolated red spots on this map are very small
surface pits, which were measured as being 20 to 40nm in diameter. These
pits are exposed subsurface damage and generally follow the linear features
on the map. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| It
is also possible to map the backside of certain wafers depending on the
level of roughness. Wafers that appear shiny and scatter only a small amount
of light can be mapped, including wafers with an oxide layer. The maps of
wafer BACK225 show scuff marks (long squiggly lines) which are caused by
handling. In addition, other kinds of features are shown which can be isolated
with the Surface and Subsurface EPBS™ maps shown below. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| The
Surface EPBS™ map shows small red spots which are particles and other
surface defects. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| The
Subsurface EPBS™ map isolates growth defects, which can be seen as
the center rings and the large outer ring. These defects will change depending
on the position of the wafer in the boule. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
A
PBS® system based on a UV laser is also available. This system uses
a 325nm laser and is useful for measuring subsurface defects on SiC and
SOI wafers and for surface measurements on silicon wafers. The map for silicon
wafer TEST21MR clearly shows three types of features:
- point defects (particles,
pits, etc.)
- scratches, and
- possible cleaning
stains
The word stain is
used here to describe the appearance of the features on the map, but in
actuality, these are areas with differing surface roughness characteristics.
This variation in roughness is extremely subtle since none of these features,
except some of the point defects, show up on the standard PBS® map
for this wafer.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| The
wafer map for TEST21MR shows a large subsurface defect in a 3" diameter
GaAs wafer. The defect, in the "T" shaped red area, could not
be detected as a surface feature in the Nomarski at 200X or with other standard
visual inspection techniques. Delineation etching revealed a high concentration
of deep damage traces in the red area of the map. Also, other wafers from
the same lot did not show the same damage characteristic. In many cases
this type of defect can be caused by debris on the back side of the wafer
that does not allow the wafer to sit flat against the pad during polishing.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Back |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
