At the turn of the century, the $200 billion semiconductor manufacturing industry across the
globe joined hands and underwent a massive transition. Maybe the last of its kind.
That transition? They made their wafers larger.
Sounds simple right? But the 300 millimeter wafer transition started in 1994,
took nearly a decade, and cost the industry billions of dollars.
So in this video, we are going to look at the semiconductor industry's momentous transition
from 200 to 300 millimeter wafers.
## Growing Up
Throughout the second half of the 20th century, the industry sought to grow
their wafers about 50% each decade without compromising on productivity and cost.
In the early 1960s,
the industry used wafers with diameters of about half an inch, or 13 millimeters.
In the 1970s, the industry transitioned to 3 and 4-inch diameter wafers.
For the 1980s, 5-inch and 6-inch wafers.
Then in the 1990s, the industry went to the metric system,
with 200 millimeter wafers, or about 8 inches. I will generally stick to the metric system.
When the 2000s came around, the 50% growth prediction meant going from 200 millimeters
to 300 millimeters - or 12 inch wafers. It had almost been like a Moore’s Law for wafers.
## Why?
But why do this? For many years, Intel led and paid for the industry's previous transitions up
to larger wafers. Their primary reason for doing so has been cost. A bigger
wafer makes advanced semiconductor manufacturing more economically viable.
To allow for a doubling of transistors on an integrated circuit every two years
required a rising amount of work and investment.
Increasing the size of the wafer helped dilute that cost by allowing
manufacturers to put more dies on a single wafer. At least, theoretically.
Moore's Law requires the entire industry to increase its productivity by 25-30% each year.
It has been calculated that wafer size transitions
have historically accounted for 4 percentage points of that 25-30%.
Intel wanted another wafer transition to help
with the yet again worsening cost situation. Yet by then,
new concerns had emerged to give people pause about whether to do this next wafer transition.
## The Last Transition
The move to 150 millimeters had been relatively smooth.
But when the industry leapt to 200 millimeters in the 1990s, things got a little out of hand.
The transition promised an over-20%
reduction in cost per die, but arguably failed to live up to those expectations.
First, it took a very long time - the longest of any prior wafer transition.
200 millimeter processing tools first emerged in the late 1980s, but it took five years before
the industry produced 200 millimeter wafers in a significant quantity. Previously, it took three.
And second, the costs got so high that it sapped away almost all of the savings. The
transition cost an estimated $5-10 billion in 1990 dollars across the whole industry,
or $11-22 billion USD today. That includes the cost of new tools, factory investments,
losses in productivity, and so on.
Things were only going to get worse. Early Estimates found that it would cost the industry
about $15 to $50 billion in 2006 dollars to complete the 300 millimeter transition. That is
about $20 to 70 billion dollars in 2022, far more than any single company can handle. Even Intel.
So despite the fact that a 200 millimeter wafer can hold 1.78 times as many dies
as a 150 millimeter wafer, companies didn’t get 1.78 times as many dies per single dollar spent.
Kind of sounds like a riddle, right? When does 1.78 not equal to 1.78?
Nevertheless, a 300 millimeter wafer can hold 2.25 times as many wafers as a 200 millimeter wafer.
Intel and the rest of the industry's leading manufacturers - Hitachi, IBM,
Motorola, Samsung and so on - still felt that a 300 millimeter transition was worth it.
## Planning
One of the big reasons why the 200 millimeter transition had not delivered on its promises was a
lack of consensus. Believe it or not, the industry could not agree on how thick the wafers should be.
Because of that, for a period of time wafer manufacturers had to produce wafers of two
different thicknesses - 725 and 735 micrometers - an unnecessary cost.
This time, the industry hashed it out early. In early 1994 - nearly a decade before the
transition’s scheduled 2001 completion - the industry set up two international consortiums:
I300I - representing the American, European,
and Taiwanese device manufacturers. And SELETE, for the Japanese manufacturers.
In July 1994, those two met up at the Large Wafer Summit in San Francisco.
There, they quickly decided on the wafer size and thickness.
They then moved on to the other technical challenges - which are formidable.
Moving an entire multi-billion dollar industry from 200 millimeters to 300 millimeters
means changing and retooling every part of the semiconductor
manufacturing process. Let us start with the wafers.
## Growing a 300mm Wafer
Figuring out how to grow, cut, polish, and deliver a pure silicon wafer crystal
so much larger than the previous generation of crystals
turned out to be one of the biggest challenges of the industry transition.
Today, we grow semiconductor-grade silicon wafers using something called the Czochralski method.
I spoke more about it in a previous video, but how it works is that you dip
a seed crystal into a pool of molten silicon called a "melt". Then you carefully pull it
out of the melt while being rotated to essentially grow the crystal.
Maybe it's just me but I can't help but think about an ice cream bar dipped into chocolate.
A 300 millimeter wafer - like Texas - is bigger. A
200 millimeter wafer crystal weighs about 90 kilograms.
A 300 millimeter wafer crystal clocks in at over three times that - 300 kilograms or 660 pounds.
That's heavier than an adult female polar bear and leads to new headaches for wafer manufacturers.
Crystals are grown with thin necks just a few millimeters wide
in order to reduce the occurrence of defects.
But for the new ones. When engineers tried to grow these absolute units with prior methods,
the crystals consistently broke their necks.
The larger volume also affects the distribution of heat throughout the crystal.
If one part of the crystal gets too hot while another part stays too cold,
then that causes thermal stress and possibly cracking. So to be safe,
you can only pull the crystal out of the melt half as fast as you would for a 200 millimeter crystal.
This lower "pulling rate" as it is called limits the wafer manufacturer's throughput.
Meaning, you can't make as many wafers in the same amount of time. Fortunately, the
half-as-fast pulling rate is not slow enough to cancel out the crystal's 2.25 times size benefits.
## Defect Engineering Crystals
The 300 millimeter wafer transition occurred at the same time
as the semiconductor industry was starting to move on to the 180 and 130 nanometer process node.
As always, this meant new design rules and defect requirements.
For this particular node generation, the first micrometer of silicon on the wafer surface
had to be completely free of all wafer defects.
So now the wafer industry found itself with the challenge of making crystals
that were simultaneously bigger and purer. And a bigger crystal
is inherently susceptible to having more defects.
There are generally two types of silicon defects. The first is a vacancy defect. This is where
you have an empty hole - called a void or a vacancy - in the silicon crystal structure.
The second is when extra silicon atoms jam together, mess up their crystal structure,
and create defects. These dislocations tend to be larger, which is more of a pain to deal with.
They might even spread across the crystal's width - which is a failure mode.
These defects happen because of the local conditions at the point
where the silicon melt solidifies onto the crystal.
Keeping control of those conditions - oxygen most importantly of all - was
extremely challenging and led to the industry considering what are called epitaxial wafers.
Epitaxy is a fancy word that describes a fancy process. Here you use chemical vapor deposition
or physical vapor deposition to produce a layer of flawlessly pure crystal silicon onto the wafer.
So, you don’t have to worry so much about wafer growth purities or the sawing possibly causing
dislocation defects. But the downside is that it is even slower and costs a whole lot too.
All of these are technically difficult challenges. And the manufacturers have
to figure them out while also achieving scale and equal or better cost than the status quo.
## Equipment
Semiconductor equipment suppliers faced several expectations when it came to this transition.
First and foremost, they had to handle and process more wafers without proportionally
increasing the tool's size. To do this, many of them started redesigning their products
to put non-critical items underneath the cleanroom floor.
Toolmakers also had to align their tools and
practices with new industry standards and larger government regulations.
And the lithography makers - on top of all that - had to do this while producing new,
more sophisticated systems for the 180 and 130 nanometers process nodes.
After the industry standards were set in 1995, the tool vendors started development
in 1996 with an eye to roll out in 1998. At the start, the industry's big tool vendors
estimated it would add about 40-70% more cost than with a 200 millimeter system.
This turned out to be an underestimate. A 2006 survey found that the equipment industry spent
$11.6 billion on the transition - 9 times more than the last transition.
This is a lot even for some of the richest companies out there.
## Redesigning the Factory
A 300 millimeter fab is just bigger. Architects need to design for higher floor and ceiling loads.
Utility piping have to be rerouted to give workers more access to items.
Tools have to move some of their guts under the floors. But I think the biggest change
was how they automated wafer handling.
Wafers are never carried around raw. They are stored in things called a
Front Opening Unified Pod, or FOUP, which preserves them in a pristine environment.
The industry standard 300 millimeter FOUP carries 25 wafers.
Fully loaded, it weighs about 19.8 pounds (9 kilograms).
Companies had already started to notice a rise in worker compensation claims and worker discomfort
complaints with 200 millimeter wafer FOUPs. So the far heavier 300 millimeter version
necessitated the automating of basically all wafer transport inside the fab.
## Automation
In their 200 millimeter fabs, Intel moved their FOUPs around using rails.
That vehicle could either be autonomously guided or manually pushed to the right equipment bay.
The 300 millimeter transition brought forth a new technology - the overhead hoist transport system
or OHT. Moving these to the ceiling allowed Intel to squeeze together the equipment bays
from 9.5 feet to 6 feet, freeing up 3.5% more space inside the cleanroom.
The downside was that overhead hoists required new software and routing algorithms
specifically for the cleanrooms. Later case studies found that manufacturers
struggled with the big software requirements involved, causing some "aberrant" behavior.
By setting industry standards on everything from fab architecture to logistics to software
integration, the industry was able to eliminate duplicative work - the Japanese managed to cut
11 different FOUP variants to just one - and accelerate wafer fab startup times.
200 millimeter wafer fabs at the time used to take 20 months to first hit wafer production.
After the wafer transition, that number was cut down to 18 months - a substantial savings.
## Completion and Future
The planning and coordination paid off.
First started in 1994, the industry largely completed its transition by 2001.
It has been 20 years since, and the industry is still using 300 millimeter wafers.
Talks to move to 450 millimeters, the supposed next generation, haven’t panned out.
As I talked about in the first wafer video, the industry doesn’t seem to have the energy
to push towards it. Equipment development costs alone are estimated to be $25 billion,
and the economic benefits are still murky.
Furthermore, it's a way different industry now. At the start of the transition,
the major industry players had been in the United States, Europe, Japan, Korea, and Taiwan.
Since then, China, Singapore, Thailand, and Malaysia had entered the game.
Intel lost its position as the driver of the entire industry. There are many other companies
now with significant say and their own incentives. Coordinating between all of them gets harder.
## Conclusion
I don't know how popular this video is going to be. But
I am fascinated by the entire notion of this decade-long,
international effort between billion dollar companies who are usually competitors.
Recently, there has been a shortage in 200 millimeter wafers.
Fabricated Knowledge picked a beautiful quote from a recent earnings call
by SUMCO management - one of the big wafer manufacturers:
> There is no way to increase 200-millimeter volume. The equipment is no longer available
and older facilities that have been idled, are obsolete. So increasing volume is not possible.
At the time, I had thought this a little weird. The market is willing
to pay for this. Why dismiss it so completely?
But after doing this video, I feel more sympathetic to the wafer-makers' plight.
The 300 millimeter wafer transition was a monumental effort. These companies moved
heaven and earth to make it happen. Asking them to roll back the clock twenty years is impossible.