Scanning Electron Microscopy (SEM)

Created by: ESW 20161129, with help from NTS and AFB'"

Introduction

This page covers the Carl Zeiss SEM at the Microelectronics Research Center (in the cleanroom). Other SEMs on campus include the FEI Quanta and Hitachi SEMs in the FNT building on main campus, and the Wasserman group SEM currently being installed. General SEM procedures used to obtain a clear image are similar (i.e. wobble, stigmation), but sample loading and equipment setup vary between SEMs.

The Carl Zeiss SEM has very good resolution (I get the best images of my 40 nm diameter Bi islands using this SEM), but does not currently have a functional EDS, and is very heavily booked. This SEM has difficulty distinguishing features smaller than 30 nm.

This wiki page currently covers top down imaging (the sample is flat or slightly tilted). An update to include cross-sectional SEM and possibly SEM-EBL (not currently a technique used by our group) would be helpful.

Training

• Ricardo holds regular SEM training sessions

• Also helpful to shadow another LASE member

• Certification with Ricardo - make sure he gives you your personal login info for the SEM computer

• Subscribe to the SEM mailing list for updates and available reservation times

• If you cancel your SEM reservation, email the mailing list

Sample Preparation

TBD

Procedure

It is very important to use the correct joystick for stage navigation

Loading sample

• Shortly before reservation starts, load stubs with samples into sample holders located in drawers across from SEM

• Log into SmartSEM software with username and password

• Vent chamber

  • Option 1: Select SpecimenChange.MLF Macro from toolbar

  • Option 2: "Exchange" button on SEM keyboard

  • These will both initiate a macro that will:

    • Lower Stage

    • Set tilt to 0

    • Vent chamber

• After chamber vents, pull open stage door about 4 inches (or about the length of your hand) (BDA 2024)

  • Using the 4 inch separation, inspect that the stage and/or wires are not scraping against the chamber

• Load sample so that flat side of sample holder is facing away from the main cleanroom, toward the flat end of the stage

  • Loading/unloading should be done with one hand (BDA 2024)

  • Do not force or twist the sample holder onto or off of the stage

• Close door gently, making sure that wires are not caught in door

• Pump down chamber

  • Option 1: Select Resume Exchange.MLF from toolbar (same icon)

  • Option 2: "Resume" button on SEM keyboard

    • Note: "Resume" button macro will prompt gun align error - choose "ignore"

    • Note 2: Macro will ask whether you have loaded a sample - choose "yes"

  • These will initiate a macro that will:

    • Pump down chamber

    • Raise stage to 20 mm

    • Turn on HV

    • Sets EHT to default values: 5 kV, aperture 30 um

  • Hold door closed during initial pumping phase to make sure there is a good seal

  • Chamber is pumped down when the Vac button goes from displaying a red X to a green check mark (~ 2 min). Vacuum should reach 1E-4 - 1E-5 Torr.

Preparing for (top down) imaging

• Raise sample to working distance

  • Open side menu and choose "Stage Navigation" to open navigation control window

  • Choose tv camera for imaging by clicking on "Signal A" under the imaging window ("Data Zone" in the SEM handout)

  • Raise the stage either by:

    • Option 1: setting the z value to 40 mm in the Go To coordinates (do not set the delta field to 40!)

    • Option 2: raising the stage with the z stage joystick (not the tilt joystick!)

  • Important - keep your mouse on the "STOP" button while using either method

  • The working distance depends on the focus of the detector, and may not change as you raise the stage

  • The gun tip is at 48 mm.

• Use x/y joystick to navigate above sample. Auxilary TV camera may be helpful if depth perception is unclear. x/y joystick is mirror image in TV camera

• Change EHT value and/or aperture size if necessary

  • I use EHT = 10 KV and working distance ~ 4 mm for Bi islands

• Change tv camera to SE2 or InLens detector

• Make sure you're looking at your sample (not the carbon tape)

Imaging (top down)

• Use x/y joystick or double clicking on target to navigate to area of interest

• Use magnification and focus knobs on keyboard to adjust focus on feature or edge of sample

• Use stigmation knobs on keyboard to adjust stigmation

• Use wobble button or window to adjust wobble if necessary

• Decrease scan speed to take high resolution image

• Freeze image when ready

• Save image - your folder will be available if you're logged in under your username

• Remember to unfreeze the image using button on SEM control panel or keyboard

Unloading Sample

• Switch back to TV camera

• Ensure that there is enough clearance between the tip of the cone and stage/samples (BDA 2024)

  • If there is not enough clearance, lower the stage manually (joystick or stage navigation menu)

• Use Exchange button or macro -this will turn off EHT, lower stage, and vent chamber

  • This macro will also undo any stage tilt, but WILL NOT undo any stage rotation. Ensure that the stage is correctly oriented before trying to remove the sample holder (BDA 2024)

• When chamber is vented, unload samples

• Use Resume button or macro to pump down chamber

• Important - Press "no" when asked about loading a new sample - otherwise EHT will be turned on and just sit there.

• Also important - make sure the chamber actually pumps down

• Enter all info in SEM logbook, including system and gun pressures

• Also important - do not log off the computer. The computer password is not generally available to users, and no one will be able to use the SEM until Rico unlocks it