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Overview

General Description

Direct physical milling of thin and thick films using a beam of accelerated argon atoms.

Specifications

• Ion beam source : inductively-coupled argon plasma (up to 2 kW), accelerated up to 1200 V in a 20+cm broad beam with currents up to 1.6 A (Kaufman & Robinson, Inc.).

• Ar+ ions neutralized using a matched electron beam current before reaching the sample.

• water-cooled rotating sample carrier can be oriented 0-90 degrees from normal beam incidence.

• Secondary ion mass spectrometer (SIMS) mounted on the system can be used for manual or automatic endpoint detection (EPD) of milled material by discerning elements based on charge/mass ratio of positive ions (Hiden Analytical).

• Sample load-lock system saves time with processing.

Technology Overview

Ion milling is a physical milling process. High kinetic energy Ar atoms are used to “sputter” material off the sample. Because there is no chemical reaction taking place between the plasma and the sample, there are a few differences compared with reactive ion etching (RIE): 1) ion milling is typically far less material-specific (selective) than RIE. As long as the kinetic energy of the Ar atoms is high enough to overcome the binding energy holding the material onto the sample surface, it will mill the material. 2) Ion milling etch rate is typically slower than RIE, because chemical reactivity along with the physical kinetic energy present during RIE make it more aggressive. 3) The milled material may re-sputter onto the sample or nearby surfaces during ion milling. Because the milled material has typically reacted chemically during an RIE process, the reaction products are often more volatile and/or chemically distinct from the original material.

Sample Requirements and Preparation

The shared carrier and mask wafers should be considered contaminated because they collect sputtered material from all users' samples.

If you care about contamination of your sample due to re-sputtering of material, you need to provide your own masks at the very least. Purchasing your own carrier from AJA will allow you to further control and reduce contamination.

• About Si wafers for masking the sample holder (Please note that all references to 6” wafers in this document should be changed to 8” wafers for the 8” tool.)

• To order your own "rotary substrate carrier" from AJA International (http://www.ajaint.com ) (email), request 8” rotary substrate carrier, use the part #  . 

About etching gold (Au) and silver (Ag): Gold (Au) is prohibited in the AJA Ion mill; do not place samples with gold in the AJA ion mill, even if it is a buried layer that will not be etched. Please discuss with Nick or the BNC staff in charge before etching silver (Ag)

Sample chuck cooling during etch: Note that thick films require high etch rates (and hence high amounts of heating), so this may mean one needs to load the sample directly on the chuck by venting the chamber (instead of using load lock). This will permit users to apply more torque and get better cooling of the chuck. However, it requires special training.

For EPD, note that argon atomic mass is the same as MgO, so the EPD is not able to sense (ionized) MgO in the large Ar ion background.

Standard Operating Procedure

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Process Control Information

Process Control Context

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Questions & Troubleshooting

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References