Leader Volume 8, Number 6
Beyer is a senior engineer at the IBM Microelectronics Division,
Hopewell Junction, New York.
His inventions have led to thirty patents.
In computer chip
manufacturing, a flat chip surface is essential because subsequent
imaging steps would be distorted if the chip would have even tiny
bumps. I discovered a
process to achieve that flat surface.
All the major silicon chip manufacturers now use that
process, whose invention couldn’t have been planned.
A silicon wafer
is produced by growing a cylinder of crystalline silicon from a
melted silicon solution. This
cylinder is then cut into thin slices, or wafers.
A mechanical grinding process removes the saw damage of the
silicon slice. The final wafer is then polished.
After processing, in order to form the many semiconductors
that become the “working parts,” the wafer is cut into small
chips, the heart of your computer.
step involves abrasion through mechanical action.
That’s a technology that’s been around since ancient
humans made jewelry. But
this kind of activity releases particles. As you may know,
processing of silicon chips requires ultra-clean environments,
since a speck of dust can interfere with the chip’s operating
wouldn’t want such a dirty chip in your computer.
Therefore, after the wafer is polished, a final brush
cleaning results in a perfect shiny surface.
In 1981, I was
asked to solve a problem in the silicon wafer manufacturing
facility. The brush
that was used to clean silicon wafers frequently became clogged
with particles, and ended up scratching the wafer.
It looked like an impossible assignment, and I had no idea
of what to do.
While browsing in
the library, I stumbled upon a five-line note in a patent review
that described a megasonic cleaning machine that uses
ultra-high-frequency vibrations to remove particles when the
vibrations are directed parallel to a surface.
I wondered if this machine might be useful to remove
particles in the wafer production process. Perhaps I could use the vibration technique, after polishing,
to shear off particles from the wafer surface into a cleaning
solution that would then carry the particles away.
an Innovation-Fostering Environment
Before I had the
chance to purchase and test the megasonic cleaner, I was asked to
work half-time on an entirely different project.
I wasn’t too happy about this situation, having to report
to two different managers. Besides
working on trying to keep particles out of polished silicon
wafers, I now had the responsibility for figuring out how to fill
the small scratches--we call them trenches--that are necessary to
separate sections within each chip in a wafer.
I was asked to try coating the silicon surface with a thin
layer of glass, which hopefully would fill the trenches and
produce a smooth, flat and stress-free chip.
The reason I was
assigned to the second project was that many others, using the
latest techniques, tried in vain to obtain a stress-free chip
trench process. So I was asked to try an old technique to deposit glass over
the etched silicon. This
method involved centrifuging a suspension of tiny glass particles
onto the wafer, and then melting the glass particles together.
Unfortunately, the trenches didn’t fill in a predictable
way and the wafer ended up with an irregular bulging glass
half-time jobs, I knew that, together, they would add up to much
more than “full-time.” I
was assigned to a small lab attached to the development laboratory
because working with small glass particles--a potential
dust-producing step--kept me away from the facilities dedicated to
clean chip processing.
I was also a
half-mile away from the wafer manufacturing area, where some of
the equipment (including the polisher and the megasonic cleaner)
was located. My working situation certainly didn’t seem
conducive to innovation. What I didn’t know then, was that one
assignment would help to solve the other.
The first project
went very well, as the megasonic cleaner got rid of all
contamination introduced during the silicon polishing step.
But I didn’t
know of any method that would create an even glass surface over
the uneven patterns that are integral to the wafer.
I feared that I would fail on this project.
Out of desperation, I turned to my fresh experience with
the polishing process.
I speculated that
simple polishing might smooth out the glass bulges.
Polishing, of course, produces particles, and particles are
I was now an expert on using the megasonic cleaner and it seemed
obvious to use that machine on polished glass-coated wafers.
So I took a gamble and walked the half mile to
manufacturing, polished the bumpy glass surface and made some
“forbidden” dust. But
I used the megasonic cleaner to remove the particles, with a
procedure that I had tried many times on bare silicon wafers
covered with polishing residue.
When I examined
the surface with an electron microscope, I was astonished as to
how flat that polished surface was.
But, I was especially surprised to see that the entire
glass surface covering the silicon wafer was clean! That
discovery, in early 1983, became even more important when we found
that a number of materials, with properties better than glass,
could fill the trenches appropriately.
In these cases, as well, the megasonic cleaner would
effectively remove particles, after polishing. A few months later,
a “whole army” of engineers now joined my efforts and, what
was originally a side project for IBM, became mainstream. This was
an important breakthrough as it led to silicon device wafers
having far greater reproducibility and quality.
Thank goodness I
was assigned two very different projects which, by fate, were
complementary to each other in respect to my invention.
Could this particular smooth surface-generating invention
have been planned? Probably
not. If it would have been planned, it would have required the
cooperation of managers and engineers, from different areas, none
of whom would have felt comfortable inserting a particle-producing
process into the sequence of clean chip-processing steps.
I’d bet that I would have been talked out of this
My story goes to
show that sometimes an activity that “shouldn’t be done” (a
dirty process near a clean site) can end up as, “Thank goodness
it was done!” I guess this is just another example of the unpredictability
of innovation. And
that’s what makes work so exciting!