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Chip making process
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Wimberleytech:

--- Quote from: ZeroResistance on January 29, 2019, 09:46:58 am ---
--- Quote from: Wimberleytech on January 28, 2019, 05:44:30 pm ---
An N-channel transistor needs N+ source and drain (the "+" indicates heavy doping of donor atoms) diffused into silicon doped with acceptor atoms so that the underlying material is doped P type.  In order to achieve desired transistor performance, that material is very lightly doped...we call it P- where the "minus" means lightly doped.  In the above, Phosphorous is typically used as a donor dopant, and Boron is used as an acceptor dopant.


--- End quote ---
The "diffused" term that you use here what does that do? I heard that ion implantation is used to for adding impurities (doping) to the silicon wafer. What does diffusion do?

Secondly you refer to the wafer being lightly doped either N- or P-.
Is that it because from what I had read so far is that the subtrate is heavily doped P+ or N+ and on top of this there is a lightly doped epitaxial layer grows P- or N-.

--- End quote ---

In the early days, diffusion was the method for creating the heavily doped drains and sources.  Yes, in modern times, it is done using ion implantation.

In modern processes, the substrate is heavily doped.  So in order to make a good transistor, a lightly doped region is required...so an epitaxial layer that is very lightly doped is deposited on top of the heavily doped substrate.  All modern processes use twin wells--one well doped P- and the other doped N-.  These wells sit inside (on top of) the epitaxial layer.
ZeroResistance:
What about Maskless Lithography systems or Direct Write systems like Mapper https://mapper.nl/.
The say that it does patterning without a mask.
So does this system only replaced the mask?
Because transistor fabrication would still need Diffusion / Ion Implanting and other processes involved in chip fabrication? How does Mapper achieve that?
Would additional equipment be needed in addition to Mapper?

TIA
Wimberleytech:

--- Quote from: ZeroResistance on January 29, 2019, 03:18:13 pm ---What about Maskless Lithography systems or Direct Write systems like Mapper https://mapper.nl/.
The say that it does patterning without a mask.
So does this system only replaced the mask?
Because transistor fabrication would still need Diffusion / Ion Implanting and other processes involved in chip fabrication? How does Mapper achieve that?
Would additional equipment be needed in addition to Mapper?

TIA

--- End quote ---
Direct-write systems suffer from throughput and throughput is EVERYTHING (well...mostly everything).
Transistor fab still needs ion implanting and the other processes.  Direct Write is just a substitute for masks.

Mapper looks interesting...will have to study that more to see if it is a breakthrough.
coppice:

--- Quote from: ZeroResistance on January 29, 2019, 03:18:13 pm ---What about Maskless Lithography systems or Direct Write systems like Mapper https://mapper.nl/.
The say that it does patterning without a mask.
So does this system only replaced the mask?
Because transistor fabrication would still need Diffusion / Ion Implanting and other processes involved in chip fabrication? How does Mapper achieve that?
Would additional equipment be needed in addition to Mapper?

--- End quote ---
In the 1980s, when 1um to 2um geometries were the state of the art, direct e-beam machines were used in a number of places for prototyping, mostly because they eliminated the mask production step. They had limited effectiveness, though. They aren't suitable for mass production, because they are so slow, so if a prototype works well, a mask set is needed for production. The mask process is different, so when the masked parts are produced the design has to be requalified, especially the analogue sections, and fast digital paths. So, direct e-beam was mostly useful for checking out logic designs quickly. These days people mostly use FPGAs to check out logic, which could be why most direct e-beam services have disappeared.

It seems Mapper is trying to make direct e-beam fast, by using a huge number of concurrent beams, so a successful prototype can be directly turned into volume production parts. It would certainly mean a lot more bugs requiring an all layers revision (ALR), would be fixed than is the case today. The cost of masks, and the time to requalify, is a huge deterrent to fixing things right now.
Wimberleytech:


--- Quote ---...The cost of masks, and the time to requalify, is a huge deterrent to fixing things right now.

--- End quote ---

Spare gates!   ;)

Requal still needed though.
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