Naked Science Forum
Non Life Sciences => Technology => Topic started by: Dr.IC on 10/03/2009 04:34:19
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Does any one have idea about VLSI circuit edit.
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Uh?
What's it all about chandan?
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I think you are talking about changing a Very Large Scale Integrated Circuit - circuit diagram. It may be a change to a circuit containing a VLSI chip (or chips) or a change to the circuit within the chip itself. This is my line of business so if you explain what you want to know I should be able to answer you.
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Uh?
What's it all about chandan?
Its about changing the circuit with in the Integrated chip.
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I think you are talking about changing a Very Large Scale Integrated Circuit - circuit diagram. It may be a change to a circuit containing a VLSI chip (or chips) or a change to the circuit within the chip itself. This is my line of business so if you explain what you want to know I should be able to answer you.
Thats great, i want to know how circuit edit is done on an chip and its effect.
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Can it be done on a chip, apart from one which is designed to be reconfigurable in some way?
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ya its possible to do circuit edit on chip, i dont know how do they do, it seems that it is sophisticated as FAB process.
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Chandan, a bit of background would help.
Some chips are simply not in any way configurable and it needs a new chip if you want to change the functions. But there are chips made that have memory built on to them. This memory can be Read Only Memory (ROM), Random Access Memory (RAM), or something in-between, which may be a memory that is written once only, or not written often, or erased/written in blocks (Flash). There are many methods of accessing such memories but that is not the question. These chips can use this memory to configure their specific functionality. Sometimes the bulk of this memory is not on the chip itself but external, as in the processor chip at the heart of the computer you are working on.
I can only think you are speaking about a Field Programmable Gate Array (FPGA). These can also use external or internal memory to "configure" them. These can be used to create quite complex logic structures. The design to be made is created by designers by writing a software description of the logic functions required using languages like Verilog or VHDL and thoroughly simulated to ensure the design conforms to the requirements. Careful timing constraints and assertions are added to this code to ensure the resulting design will meet its speed requirements and to aid the subsequent software processes. The design is then "Synthesised" for a particular cell library. For an FPGA this is supplied by the manufacturer and is a range of minimal logic structures that are fully characterised over process variation and temperature and for various loading states. The resulting output (which often takes a few iterations) can then be physically applied to the FPGA. Hopefully the FPGA will then work as intended. If it does not, then it can be re-programmed to iron out bugs.
FPGAs come in various sizes and with with some software free. The synthesis software (if specific to the FPGA) is heavily subsidised compared with general purpose synthesis tools. General purpose IC design tools cost a lot of money! The bigger FPGAs use quite modern fine geometry processes to pack a lot on to each chip and are very expensive. They are great for prototyping and smaller volume production but not for very high volume where a conventional dedicated chip (standard product or custom) would be more cost effective.
As far as "circuit edit" on-chip, it is sometimes possible to make small changes to a synthesised design without the need to resynthesise the whole design. For an FPGA this will still require the FPGA to be reprogrammed but it cuts out a lot of work. For full chip designs the circuit is hard wired and once the chip is made it is a lengthy and costly process to make a new one. The latest chips (in sub 45nm technology) are estimated to cost about $75m to develop and bring to production status. It is best to get them right but with 100s of millions of transistors on each device this is not a trivial exercise.
As an aside, very few large logic designs have anything resembling a circuit schematic now. All the design is defined by the HArdware Description Language (HDL) be it Verilog or VHDL. Analogue circuits are still done with schematics though.
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Just to add to this, chips can also be modified in a small way by using a Focussed Ion Beam to cut tracks and deposit other tracks. It is limited to very small changes and is a manual process that requires some skill. The package has to have a hole etched in it (if plastic) or the lid removed (if ceramic) so that the die can be accessed in the area requiring the modification. This is handy as a one-off test that a proposed modification works and can be valuable in reducing risk in a follow-up design.
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We used to install EPROMs as security devices but they're the only type I know of. We put a code into the software and the same code on the EPROM. We used them as a type of security dongle in that respect.
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I want to know how tracks are cut and deposited and how to make a hole. and which metal is used for forming the tracks.
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It is not a DIY activity :-) You may need a plasma etcher to remove the plastic. You can also use acids in a wet etch environment - boiling sulphuric works. Both these methods can end up removing all the plastic though, which tends to result in the package pins falling off. Masking the plastic (where you don't want the etch), using a directed ion beam, or (it can be done) by dropping acid on the plastic carefully, are methods that can be employed. You then need a minimum of a focussed ion beam etcher. You, of course, need a detailed plot of the chip's structure close to where the modification is to be carried out, and a plan of what to do. The FIB is used to erode through the layers of SiO2 and metal tracking where required. Multi layer metal processes can be a problem because the track you wish to cut maybe masked by higher levels of metal which you don't want to cut. It is not always possible to do a required modification and, even if possible, can have a variable success rate. Selective etching of some materials is also possble. The FIB can also deposit material to connect nodes. But be aware that the material deposited is very thin and, unlike the metal, will have a much higher resistance.
I can recommend a UK company who do this work at a reasonable cost if you wish. They charge by the hour, but even for a simple change, it will probably cost a few thousand pounds to get a few devices done. And you need to provide all the data in some detail.
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Which Metal is used to join the nodes. What will be the approximate resistance.
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Various metals can be used. I think it was Tungsten on the last FIB mod I had done. I don't remember the exact resistance although you have a thicker layer deposited to reduce the resistance if this is important, but don't expect to get close to the resistance of normal interconnect. I think it was in the region of a few hundred ohms/square (compared with a few tens of milli-ohms/square for normal interconnect metal.
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Hi graham,
I googled for FIB I could find some material and was amazed, now i want to know more about that, i am still confused that how the thin metal is deposited. [???]
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I have not personally operated a FIB machine myself though I have had contract companies do such work many times. A reasonable description is on wikipedia:
http://en.wikipedia.org/wiki/Focused_ion_beam
It explains that deposition is done by "ion beam induced vapour deposition". To elaborate, the beam is controlled so as to scan the surface in the area where deposition is to be made, so it is not required to deposit over a wide area (as with normal vapour deposition) and then use any masking processes to remove the unwanted depositions. The same technique is used in ion beam lithography but on a larger scale. Basically Tungsten Hexacarbonyl vapour (for example) is present in the chamber with the sample to be worked on. The compound gets adsorbed onto the material's surface and the impacting ions (usually Gallium) causes the tungsten to be deposited.
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Ok,i think scanning is same as raster scanning in electron tube, but how does ion beam induced vapour deposition will be done.
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Chandan, you have reached the point where I am having to do research on Google for you. I have found a very good summary of FIB techniques here:
http://www.absoluteastronomy.com/topics/Focused_ion_beam
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what about using CPLDs?
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what about using CPLDs?
Can i know what you are expecting.
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Hi Graham
The link was useful, i need favor from you,
"A FIB can also be used to deposit material via ion beam induced deposition. FIB-assisted chemical vapor deposition occurs when a gas, such as tungsten carbonyl (W(CO)6) is introduced to the vacuum chamber and allowed to chemisorb onto the sample. "
This i found in the link you send it to me,
i want to know how ion beam induced deposition is done using (W(CO)6).., i want the chemical equation.
i thought you will be having good contacts with the person working on FIB, i thought you can get some details. i tried in net i dint get.
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I am afraid the people I know are experts in using the equipment but only have a basic understanding of the chemistry involved. I think it is rather complex and not wholy understood. A quite good paper on the subject from 1991 is here:
http://www.iop.org/EJ/article/0953-8984/3/S/032/cm910a32.pdf?request-id=5DA8FC08-13A7-11DE-A4F5-29286948AA0C
It shows that it is not a simple effect bt that there are resulting deposits of Gallium and compounds formed with the Silicon (as you may expect), but also Carbon deposits and compounds.
There is a PhD paper from MIT which goes over a lot of the basics. If you search in Google for:
"Ndno-cellular Microstructure Evolution In Ion-Induced Chemical"
You should find the reference and download the paper. I think the "Ndno" should be "Nano" but this is exactly how they have mis-spelled it. I cut and pasted this so you should copy this phrase exactly.
I am not a chemist so my knowledge is superficial about the chemistry involved. In fact I think a lot of the chemical processes involved are not wholly understood and much of the developmental work is empirical.
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The topic huge.., and an unending story...
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The topic huge.., and an unending story...
that is life>>..... though isn't it?
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Any free e-book available for this topic?
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If you are thinking of trying your hand on a little 'reverse engineering' here then that seems quite hard Chandran. I think you need advanced machinery to 'scan' the chips layers and then you need to know an awful lot of how the 'logic circuits' can be expected to look. http://en.wikipedia.org/wiki/Microfabrication.
Take a look here http://www.flylogic.net/blog/
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Chandan, you have never actually said what you are trying to do or from what base of knowledge you are starting. I have tried to answer your questions fully without knowing this, but to help further would involve me in researching the web, which you could do equally well. If you have a specific task in mind, then say what it is and I may be able to point you in the right direction. I don't know any free e-books on FIB modification.
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Chandan, you have never actually said what you are trying to do or from what base of knowledge you are starting. I have tried to answer your questions fully without knowing this, but to help further would involve me in researching the web, which you could do equally well. If you have a specific task in mind, then say what it is and I may be able to point you in the right direction. I don't know any free e-books on FIB modification.
Fine i am trying to learn about FIB circuit EDIT and i got few study materials in web. and i want to understand chemistry behind FIB edit.
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If you are thinking of trying your hand on a little 'reverse engineering' here then that seems quite hard Chandan. I think you need advanced machinery to 'scan' the chips layers and then you need to know an awful lot of how the 'logic circuits' can be expected to look. http://en.wikipedia.org/wiki/Microfabrication.
Take a look here http://www.flylogic.net/blog/
Its not about reverse engineering.. its about circuit edit in chip.
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Chandan, looking at the detailed chemistry is not my field of expertise I'm afraid and, as I said, much of the development in this field is empirical. I just use it when I need to and I am just about to get some done in the next week or two! Is it out of just curiosity that the chemistry of this is of interest or do you have a practical goal on mind?
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I have plans of working practically.
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What is difference between e-beam lithography and ion beam lithography?
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e-beam lithography scans electrons across a surface coated with a "resist" that changes its structure where the beam impacts. This allows subsequent selective etching of the resist, thereby patterning appropriately. Ion-beam is often used to directly selectively etch the surface material.
Chandan, I don't wish to put you off your pursuit, but you seem to be starting from a base of knowing little about this very sophisticated technology and wish to do something "practical". Have you thought about taking a course at a university to study the subject in detail? If you have a degree in physics or electronics (for example) you could probably find a university with suitable facilities to pursue a post-graduate course in this field. There is a good deal of interest in the subject and there may be semiconductor companies or equipment manufacturers who may help fund a research project.
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Chandan, I don't wish to put you off your pursuit, but you seem to be starting from a base of knowing little about this very sophisticated technology and wish to do something "practical". Have you thought about taking a course at a university to study the subject in detail? If you have a degree in physics or electronics (for example) you could probably find a university with suitable facilities to pursue a post-graduate course in this field. There is a good deal of interest in the subject and there may be semiconductor companies or equipment manufacturers who may help fund a research project.
I have already done masters in science with electronics, is there any course that can help me...
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Where are you based? The University of Surrey (Guildford, England) has an Ion Beam research group for example. If you have a masters and wish to do a PhD, you could write to them to see if they have a vacancy.
There are many universities that have related activities. You can type "ion beam lithography university research" into Google as well as I can :-)
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Thanks for info... lets see...
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should go for institute for studies
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Hi graham
I have found a company which has a FIB facility in India. I want to know how the company could help me.
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If it's a company, I would start with the precept of how you think you could help the company. They would not regard themselves as a charity.
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I will try going for industrial visit.