Micromirror LithographyMicromirror Lithography

David ChenDavid Chen

EECS 277EECS 277

OverviewOverview

What is Lithography?What is Lithography?

What are Micromirrors?What are Micromirrors?

Successful ResearchSuccessful Research

FutureFuture

What is Lithography?What is Lithography?It is the backbone of nearly all It is the backbone of nearly all semiconductor device fabrication processes.semiconductor device fabrication processes.

It allows for high precision and tiny devices.It allows for high precision and tiny devices.

It allows for mass production.It allows for mass production.

For the most part, it removes human error For the most part, it removes human error from the manufacturing process, giving high from the manufacturing process, giving high yield production.yield production.

What is Lithography?What is Lithography?

The procedure for lithography is as follows:The procedure for lithography is as follows: Start with a waferStart with a wafer Deposit or grow layer of desired materialDeposit or grow layer of desired material Spin coat photoresistSpin coat photoresist Pattern photoresist by exposurePattern photoresist by exposure Etch layer underneath or deposit/grow new Etch layer underneath or deposit/grow new

layerlayer Remove photoresistRemove photoresist RepeatRepeat

What is Photoresist?What is Photoresist?

Light sensitive materialLight sensitive materialChanges molecular bond after Changes molecular bond after exposure to certain wavelengths exposure to certain wavelengths of lightof lightUsed to make planar patterns Used to make planar patterns determined by photomasksdetermined by photomasksProtects layers underneath during Protects layers underneath during etchingetchingCan be easily removed after each Can be easily removed after each processprocess

Example of LithographyExample of LithographyA familiar device: CMOS inverterA familiar device: CMOS inverter

LinkLink

7 different photoresist patterns7 different photoresist patterns

7 different photomasks7 different photomasks

Very simple deviceVery simple device

Masks Cost How Much?!?Masks Cost How Much?!?

Costs per mask-setCosts per mask-set

65nm ~ $1million65nm ~ $1million

45nm ~ $2.2million45nm ~ $2.2million

32nm ~ $4million32nm ~ $4million

28nm ~ $8million28nm ~ $8million

Bearable for high volume manufacturersBearable for high volume manufacturers

Outrageous for small companies or prototypingOutrageous for small companies or prototyping

Masks also deteriorate after use!Masks also deteriorate after use!

Why are masks so expensive?Why are masks so expensive?

Very high resolution structures require Very high resolution structures require expensive processes such as electron beam expensive processes such as electron beam etching or laser etching (also lithography)etching or laser etching (also lithography)Unique pattern means masks are custom made Unique pattern means masks are custom made per client orderper client orderNeed an alternativeNeed an alternativeWhat other things produce high resolution What other things produce high resolution images…images…AKA high definition images…AKA high definition images…AKA HD…AKA HD…

We Already Have the Technology!We Already Have the Technology!

Made famous by Texas Instrument’s DLP Made famous by Texas Instrument’s DLP (digital light processing) televisions(digital light processing) televisions

DMD- digital micromirror deviceDMD- digital micromirror device

Project high resolution imagesProject high resolution images

What Are Micromirrors?What Are Micromirrors?

MEMS (Micro-electro-mechanical systems)MEMS (Micro-electro-mechanical systems)

Array of millions of mirrors on a tiny chipArray of millions of mirrors on a tiny chip

Each mirror can be independently controlledEach mirror can be independently controlled

On/Off statesOn/Off states

TV vs. Maskless LithographyTV vs. Maskless Lithography

Even though they’re HD, TV pixels are still Even though they’re HD, TV pixels are still way too big for lithographyway too big for lithography

We are trying to pattern photoresist on the We are trying to pattern photoresist on the sub-micron scale!sub-micron scale!

Need a HUGE lens to focus the array to a Need a HUGE lens to focus the array to a smaller scalesmaller scale

Making a huge lens is hard.Making a huge lens is hard.

One Solution from MIT: ZPALOne Solution from MIT: ZPAL

Using an equal number of Using an equal number of array of diffracting lenses array of diffracting lenses fabricated by lithography, fabricated by lithography, each beam of light can be each beam of light can be focused individually.focused individually.

Feature sizes can be Feature sizes can be much smaller than the much smaller than the beam width!beam width!

Results from testResults from test

Well defined structuresWell defined structures

Low roughnessLow roughness

Features on spot size scaleFeatures on spot size scale

Done using UV lightDone using UV light

Future ImprovementsFuture Improvements

Smaller wavelength lightSmaller wavelength light EUV (extreme UV) 120nm-10nmEUV (extreme UV) 120nm-10nm X-Ray 10nm-1pmX-Ray 10nm-1pm

Higher refractive mediumsHigher refractive mediums Liquid immersed fabricationLiquid immersed fabrication

= Smaller spot size= Smaller spot size

Benefits of Micromirror LithographyBenefits of Micromirror Lithography

Programmable “mask”Programmable “mask” Vs. permanent photomaskVs. permanent photomask

No cost for prototype masksNo cost for prototype masks Vs. $millions per setVs. $millions per set

Instant mask productionInstant mask production Vs. weeks to months per setVs. weeks to months per set

All of the above = Cheaper!All of the above = Cheaper!

ResourcesResources

http://http://www.eetimes.com/showArticle.jhtml;jsessionidwww.eetimes.com/showArticle.jhtml;jsessionid=ONC4WJBQYCVL0QSNDLRSKHSCJUNN2JVN?articleID=21110=ONC4WJBQYCVL0QSNDLRSKHSCJUNN2JVN?articleID=2111002240224http://jas.eng.buffalo.edu/education/fab/invFab/index.htmlhttp://jas.eng.buffalo.edu/education/fab/invFab/index.htmlhttp://www.eetimes.com/http://www.eetimes.com/showArticle.jhtml;jsessionid=ONC4WJBQYCVL0QSNDLRSKHSCJshowArticle.jhtml;jsessionid=ONC4WJBQYCVL0QSNDLRSKHSCJUNN2JVN?articleID=211100224UNN2JVN?articleID=211100224http://nanoweb.mit.edu/zpal/Presentations/SPIE_2005_web.pdfhttp://nanoweb.mit.edu/zpal/Presentations/SPIE_2005_web.pdfhttp://nanoweb.mit.edu/zpal/Presentations/EIPBN-2004-Alpha.pdfhttp://nanoweb.mit.edu/zpal/Presentations/EIPBN-2004-Alpha.pdfhttp://nanoweb.mit.edu/zpal/Presentations.htmlhttp://nanoweb.mit.edu/zpal/Presentations.htmlhttp://nanoweb.mit.edu/zpal/Presentations/EIPBN-2004-SSP.pdfhttp://nanoweb.mit.edu/zpal/Presentations/EIPBN-2004-SSP.pdf