So these trigate devices were first introduced at the
22 nm
Technology.
And I want to make a very profound statement here, predicting the future.
That, you know, going forward, as you know, you go
from 22 nanometer to 14 nanometer or 10 nanometer technology.
What, what, what I'm saying is that these devices going forward will
become taller and they'll become thinner. So in a lot
of ways, in a way, fun way these devices, these trigate devices, they, they are
resembling human, human nature or, you know,
as human beings we all want to be tall.
And we want to be, you know, we want to be skinny and we want to be thin.
So in a lot of ways you know, these devices are in a very fun the way
they, they they want to resemble the human nature that you know, as they grow up.
As the year passes by
they want to be taller and they want to be thinner and you know
that creates a lot of challenges in terms of processing these devices.
But you know, let me try to explain why, why this is the
case, why you want to be taller and why do you want to be thinner.
So, let me evoke back this analogy that we had
used earlier that you know, we have two beakers essentially.
You know, one beaker is the source,
which is the source of carriers or electrons, and the
other beaker is a drain which is to connect these carriers.
And you have this gate which acts like a nozzle which
controls the flow of electrons from the source to the drain.
So, you know, going forward in technology you know, as you go from 22
nanometer technology to, you know, 14 or
10 nanometer technology, you will be scaling
your gate length.
So, you know, currently our gate length of
22 nanometer technology is actually 30 nanometer gate length.
And going forward you'll be, you know, reducing your
gate length to say, you know, 25, 22, 20 nanometer.
So as you are, you know, you're reducing this gate length and you are
scaling your gate, the device you know,
the electrostatics of this device is only maintained
when you shrink down this nozzle, too.
See, what I am saying is, you know, if you are shrinking your gate
length, you need to shrink this nozzle width too to maintain this same gate control.
So to maintain the same effectiveness of this nozzle you need
to scale both your gate length as you're scaling your gate length.
You need to scale the width of this
nozzle
Or you need to scale the thickness of this channel material
And let me illustrate this further so you know.
And this scaling law actually depend upon the nature of the device.
So, say a double gate device it has pretty
decent electrostatics. So as you're scaling your gate length.
You need to scale your length of your, as you're scaling your gate
length, you need to scale your thickness of this,
of this channel material as two-third of the gate length.
for a trigate device, it has better electrostatic control as
compared to the double gate device.
So, this scaling of this silicon thickness is slightly relaxed.
So you know when you are scaling your gate length, you need
to keep your, your silicon thickness roughly proportional to your gate length.
So you know going from 2 3rd you are actually going to one.
So you know you're slightly relaxing on this thickness requirement.
for a gate all around device now, which has you know even better electrostatics, this scaling
law now becomes, you know, your need to keep your thickness of your silicon.
Or you know, the diameter of your wire you know, it could be maximum of twice your
gate length, so now you are scaling with twice
your gate length in this gate all around twice.
And you know, one of the homework
problems, I, I've right now you're simply stated these
formulae
one of these homework problems.
You'd be actually deriving this how the t silicon depends, you
know what is the function dependence on the gate lens for all these three device.
So there will be homework problem where you'll actually be deriving this.
So, you know that explains, you know, now so as
you scale your gate length you need to scale your,
your you know, the thickness of your channel material.
So that explains, you know, why these devices need to
become thinner, or you know, why they need to be skinnier.
So, you know, going forward, you would like to scale your gate
length, because then you're continuing your
Moore's law you know, improve your performance.
And so you know you need to scale your enable
your gate lens scaling your you need to scale your
silicon thickness so, so that's why you need to
going forward you need to make these devices thinner.
Right, so, so now why do you need to make them taller, you know?
Why, why tall?
So tall is very simple, you know. The taller you have your device, you can
pack a larger amount of current in the same area density.
So, you know, for example, you have this device and, you know, if I make it twice
as tall, you know, I keep my area footprint on my substrate the
same but now, you know, I have twice, roughly twice the amount of surface area.
So you know, the taller I make the device, the more you
know, the more on current I can pack in the same area, right?
So on
current per area for you know. It increases.
So one way to enable further performance improvement or to enable
current improvement is you know, to keep on making these devices taller and taller.
So you know, another so these,
these fin, FinFET devices essentially allow another handle to Moore's law.
You can improve your on current to it.
You can, you know, you can decrease your gate length, right?
Or you can increase your fin height, right?
So, both of these demands that, you know, you, you need to, to enable to decrease your
gate length, you know, you need to, you know, scale your, scale your fin width.
So you need to make them, you need to make them thinner and
you know, to increase the on current by increasing the fin height.
Now, you need to make them taller, so that's why,
you know, going forward, these devices, I'm predicting is, sorry.
So I'm predicting that these devices will be taller and they will be
thinner. And that looks very nice on this cartoon
but this is a lot of processing challenges.
So, you know, as you can expect, you want to deposit a conformal
gate oxide on this you know, very high aspect ratio fin, you know.
As you are making them thinner and
taller, you are increasing your aspect ratio, right?
So that introduces a lot of process complexity
and process challenges that we will discuss in the subsequent class.