[labnetwork] LED Lights for Lithography

Sun Feb 23 11:55:53 EST 2020

> I have to say that I was very interested in responding to your first email, as I am looking for ways to eliminate the use of mercury arc lamps to LEDs.... 

I could work on that problem as well.  It's a worthy cause, on more than
one front.   

In general terms, I am currently working on a range of scientific
applications of advanced LED technology.  I thought illumination of
lithography environments (the rooms), critical as it is, is a perfect
fit for this focus.  You have identified another area that would warrant
attention. 

I'm happy to look into it and do the necessary research and prototyping.
 All I need is specifications.  If anyone can help with that I'll take
it from there. 

Thank you, 

-Martin 

---

On 2020-02-23 04:37, Mario Portillo wrote:

> I have to say that I was very interested in responding to your first email, as I am looking for ways to eliminate the use of mercury arc lamps to LEDs.... 
> 
> Anybody out there with the same thought let me know, 
> 
> Regards 
> 
> Sent from Yahoo Mail for iPhone [1]
> Mario Portillo, hbtusainc at yahoo.com 
> On Sunday, February 23, 2020, 11:40 AM, martin at algoshift.com wrote:
> 
>> Based on a couple of responses it looks like I did a confusing job of 
>> explaining what I am working on.
>> 
>> I am focusing on lights to illuminate the lab, the room, not to cure 
>> PMMA.  So, yes, this is about lights on the ceiling.
>> 
>> Also, I said "above 500 nm" when I was thinking frequency.  I should 
>> have said "below 500 nm".  The point is, as I understand it today, the 
>> goal is to not have much energy in the blue and UV range of emissions.
>> 
>> Sorry for the confusion.
>> 
>> Thanks,
>> 
>> -Martin
>> 
>> ---
>> 
>> On 2020-02-21 23:55, martin at algoshift.com wrote:
>>> I am currently working on the development of LED-based lights for
>>> lithography applications.  I came across this list and was kindly
>>> allowed to join.
>>> 
>>> I have a background in high-performance, high accuracy LED-based
>>> applications going back some twenty years.  In addition to that I
>>> worked in aerospace engineering, robotics and other work I can't talk
>>> about (most recently, SpaceX).
>>> 
>>> At this stage in my new mission I am trying to confirm what I have
>>> learned in order to start developing a few prototypes for testing.
>>> This is what I know and don't know so far:
>>> 
>>> - Energy above 500 nm should be below 0.001%
>>> - Operator metamerism doesn't seem to be much of a concern in these
>>> environments (?)
>>> - Outgassing is not desirable (I don't have any kind of a
>>> specification for this)
>>> - No specification on acceptable flicker
>>> - No specification on required efficiency (Lumen/Watt)
>>> - No specification on the amount of light required, either:
>>> - Illuminance (intensity of light on a surface, lux) or,
>>> - Luminance (light energy emitted, lumens)
>>> 
>>> Frankly, there really isn't very much data out there.  It also seems
>>> that semiconductor companies keep their lithography illumination
>>> requirements somewhat close to the vest.  At least this is what I've
>>> come across.  I wonder if this is because these kinds of
>>> specifications might reveal process details?  Don't know.
>>> 
>>> The three main trades I have in front of me at the moment for this 
>>> design are:
>>> 
>>> - White LEDs with carefully selected film or coating-based filter to
>>> cut blue + UV
>>> - Green and Red LEDs only, no blue; filtration is still needed
>>> - A combination of carefully selected white LEDs with low spectral
>>> power above 500 nm along with, perhaps, green and red to enhance;
>>> filtration still needed
>>> 
>>> To clarify, the Green+Red LED option still requires filtration because
>>> green LEDs produce some energy above 500 nm.  If I am to take the
>>> 0.001% specification to be true, an optical filter would still be
>>> required.
>>> 
>>> White LED's, which, of course, are nothing more than blue LEDs with a
>>> phosphor coating are the most readily available high efficiency units
>>> in the market.  Frankly, if high light output at the lowest possible
>>> cost is a requirement it is hard to beat them with a combination of
>>> red and green LEDs.  That said, depending on how they are selected, a
>>> significant portion of the spectral power they emit will have to be
>>> converted into heat at a filter or bad things will happen in the lab.
>>> 
>>> The third option involves selecting very warm white LEDs that have
>>> almost no blue spike.  This means less heating of the filter element
>>> and, likely, longer life.  This could be an interesting solution.
>>> 
>>> Plastic film based filters degrade over time, particularly if there's
>>> a lot of heating due to having too much energy in the undesirable
>>> portion of the spectrum.  This is where thin film deposition
>>> (sputtering?) could exhibit far more favorable band-pass
>>> characteristics as long a longevity.  Cost, of course, could be an
>>> issue.
>>> 
>>> I am very familiar with material out-gassing issues in the context of
>>> aerospace applications.  Not so for lab usage.  Understanding where
>>> these limits might lie would be very useful.  The perfectionist in me
>>> wants to design a T5-class 4 ft LED light fully encased and
>>> appropriately sealed in a durable glass tube that is both internally
>>> and externally coated to not pass light above 500 nm.  At the same
>>> time, I do understand that a real solution has to fit a budget as well
>>> as technical specifications.  Not sure where that intersection lies
>>> but I am aware of it.
>>> 
>>> I introduced a term above that might not be familiar to everyone here;
>>> observer metamerism.  This is a by-product of the spectral power
>>> distributions of light, reflection and the human vision system
>>> interacting in such a way that two colors that are different might
>>> appear the same (or, in general, you have trouble discerning colors
>>> that are easy to see under different conditions).  If you've ever
>>> tried to determine if a steak is well done under a typical white LED
>>> light and could not, that's observer metamerism.  Mitigation requires
>>> "filling in" the emitted spectra in areas relevant to the task at
>>> hand.
>>> 
>>> This is why I asked myself this question in the red+green LED case.
>>> Both of these have narrow emission spectra.  Our brains can function
>>> with this kind of light and, yes, we will see it as yellow.  However,
>>> any colors in the portion of the visible spectrum lacking energy will
>>> become challenging to deal with.  It's like being color blind.  Given
>>> that lithography labs are already built to work with yellow light, I
>>> find myself wondering how much of a problem, if any, might be posed by
>>> observer metamerism in the case of the proposed red+green LED
>>> solution.
>>> 
>>> I think that's the basics at this point.  I would appreciate any and
>>> all feedback, questions and even a good shove in the right direction.
>>> 
>>> Thank you,
>>> 
>>> Martin Euredjian
>>> AlgoShift, LLC
>>> Los Angeles, CA
>>> 661-305-9320
>>> 
>>> _______________________________________________
>>> labnetwork mailing list
>>> labnetwork at mtl.mit.edu
>>> https://mtl.mit.edu/mailman/listinfo.cgi/labnetwork 
>> 
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