DRIEandLIGATechnology

ByBrook Degef and Hannah ParkENEE 416October 13, 2009

What is DRIE?

Deep reactive-ion etching(DRIE) is a very anisotropicetching process.

Used to achieve high-aspectratio (up to 50:1).

Selectively enhancing theetching rate at the bottom of thetrench while inhibiting lateraletch rate.

Etch depths of hundreds ofmicrons can be achieved withalmost vertical sidewalls.

Common RIE Setup

A RIE consists ofTwo electrodes (1 and 4)Electric field (3)Surface of the samples (5)Plasma that contains bothpositively and negatively chargedions (2)Surface of the samples (5).

These ions are generatedfrom the gases usually O2and CF4 pumped in.

Types of DRIE

Two Types of processes Cryogenic and Bosch.

CryogenicThe wafer is chilled to −110 °C.The low temperature slows down the chemical reaction that produces isotropic etching.However; ions continue to bombard the horizontal surfaces and etch them away.

Draw backAt this very low temperature the mask could break.By-products have a tendency of depositing on the nearest cold surface, i.e. the substrateor electrode.

As a result of these drawbacks this techniques is not commercially viable.

Types of DRIE continued

BoschThe primary technology is based ontwo different gas compositions arealternated in the reactor.

The first gas composition creates apolymer on the surface of thesubstrate, and the second gascomposition etches the substrate.

To etch through a 0.5 mm siliconwafer, 100–1000 etch/deposit stepsare needed.

Pros/Cons

ProsHigh aspect ratios (up to 50:1).Deep etching (10µm-700µm).High etch rate (4-20µm/min). +/- 0.5 deg sidewall angle control.

ConsNew tools cost $½m to $1m.Only single wafers are processed at a time.

Applications

Automotive industry Pressure sensors Accelerometers Miniature gyroscopes

Digital light processing (DLP)chips for video projectionsystems in industry and athome.

Parts of printer ink jet heads.

What is LIGA?

Stands for lithiography, galvanoformung andabformung which when translated meanslithography, electroplating, and molding respectively

Newly developed process that uses thickphotoresists as molds which are subsequently filledwith metal plating processes.

Two main types of LIGA techniques:– X-RAY LIGA which uses X-rays to create high-aspect ratio

structures– UV LIGA which creates lower aspect ratio structures.

LIGA setup

Photoresist (usually PMMA -polymethyl methacrylate) isplaced onto substrate. Thephotoresist must have a highselectivity and be relatively freefrom stress when applied inthick layers.

The synchrotron emits high-power, highly collimated X-rays.This high collimation permitsrelatively large distancesbetween the mask and thesubstrate.

LIGA setup continued

In the electroplating step,nickel, copper, or gold isplated upward from themetalized substrate into thevoids left by the removedphotoresist.

The photoresist is strippedleaving the metal structures

The metallic molds can bereplicated and reused.

Types of LIGA

X-ray LIGA which uses X-rays to create high-aspectratio structures

– Uses x-rays to expose– More expensive but precise in features– Heights up to 1 mm and a lateral resolution down to 0.2 µm.

UV LIGA– Uses UV light to expose– Cheaper and more practical to use– Lower aspect ratio features

Pros/cons

Pros– Feature sizes of several micrometers with structural height

of several 100 µm to several 1000 µm– Extreme parallelism/verticality of sidewalls– Also, thickness allows for strength and durability for many

different situations and environments Cons

– X-ray masks are expensive to produce– Machinery is expensive (for X-ray)– Requires a short-wavelength x-ray source to expose the

photoresist.– Can be a slow process

Applications

Production of high-precision parts for MEMS. Motor parts that require rotation or movement are easily

created with LIGA technology because of the precise andcareful detail it is able to produce.

Micro-opto-electromechanical system (MOEMS). Sensors, x-ray optical components, and 3D high powered

microwaves all use components that are developed by theLIGA process.

Microfluidics. Devices in this field can be used for throughputscreening and therapeutic drug delivery.

Biotech systems, optical systems, and ink jet printers all requirecomponents that can be fabricated by LIGA technology.

Pictures

A 517 µm tall copper coplanar waveguide Figure 1. A nozzle for uranium enrichment

References

http://cleanroom.byu.edu/rie_etching.partshttp://en.wikipedia.org/wiki/Deep_reactive-ion_etchinghttp://www.mrs.org/s_mrs/sec_subscribe.asp?CID=16750&DID=231825&action=detailhttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V44-4B0NY3W-1&_user=961305&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1041808857&_rerunOrigin=google&_acct=C000049425&_version=1&_urlVersion=0&_userid=961305&md5=a0d7d3c426cd8dc233d0722ea0dc649e