|
Highly Automated Wafer Scriber Requires Minimal Service
and Engineering Support
After device fabrication completion on
a semiconductor wafer, engineers
must cut the wafer into individual circuits
and devices. Engineers carry out this dicing
and singulation process using a very
thin, diamond-coated saw blade; however,
engineers must dice some devices and circuits
using scribe dicing technology.
In this process, the system draws a
sharp diamond tip across the wafer surface
between the circuits and devices
along a crystallographic plane direction
to form a scribe line with precise positioning
and depth. The system then
breaks and cleaves the wafer along this
scribe line.
Micro Processing Technology designed
a high-precision scribe-dicing system
to run in a reproducible manner,
making it easy to set up and maintain
scribe processes. The system processes
up to 200-mm diameter wafers.
Operation
The system, which uses closed-loop force
control, has six motion axes and an additional
axis for the input from the force
sensor. There are four linear motor and
encoder stages in a gantry configuration,
with a vertical stage attached to the cross
stage. There also are two rotary stages.
The force sensor is composed of an air
bearing, a 0.1-micron linear encoder, and
high-precision springs. When the system
is in operation, the scribe tip position is
controlled first to bring it to the wafer surface.
The system then switches the feedback
to this axis to the encoder on the
force sensor for direct PID force control.
The system performs motion control
using National Instruments’ (NI) Lab-
VIEW graphical development environment
and an NI PCI-7356 motion control
board. Engineers can upgrade motion
controllers in functionality by loading the
latest version of the driver software, which
in turn updates the firmware onboard the
controller. This increased the scribe forcesampling
rate from about 60 times per
second to 4,000 times per second.
Machine vision was used to position the
scribe tip correctly between the devices on
the wafer surface. The engineers performed
this operation using LabVIEW and
two FireWire cameras running on an NI
PCI-8252 board. The first camera determined
the wafer location on the vacuum
chuck. The second camera was mounted
on a 12X-zoom microscope. When viewed
on a 17-inch LCD monitor portion, this
configuration provided a maximum image
magnification of about 800 times. With this
high magnification, the scribe tip positioning
can be viewed in the scribe street center
to a precision of about 1 micron.
More Information
Contact the author, Mr. P.C. Lindsey, president
of Micro Processing Technology, Inc.,
Lafayette, CA, at pclindsey@microptech.com.
Visit http://info.ims.ca/5292-330 for more
information on the Model 24-7 High-Precision
Scribe Dicing System. Visit National Instruments
Corp., Austin, TX, online at
http://info.ims.ca/5292-331.
|
