Purpose, location and technical specifications

Figure 1: 'HF vapour phase etcher 01' is not in the cleanroom yet

The 'HF Vapour Phase Etch' machine (a Primaxx uEtch from SPTS) is a single wafer (or pieces) HF vapor etch machine designed for etching sacrificial silicon oxide layers, primarily to release silicon microstructures in MEMS devices. The process uses anhydrous hydrogen fluoride (HF) gas as etchant and ethanol vapor as catalyst. In this way silicon dioxide can be etched in a dry process and the problems associated with wet etching is avoided (small structures collapse when they are underetched due to surface tension of water).

The etch gas and catalyst easily diffuses into "hidden spaces" making e.g. long undercuts, membrane and resonator release etches feasible.

Preliminary steps

Layout preparation

You need to import your layout in Elphy before patterning your sample. The software contains a proprietary layout editor in which you can import, view and edit your designs afterwards.

The editor reads and produces single .gds or .csf files. To design your pattern you can use L-edit, Clewin or other CAD software. Try to limit yourself to a simple pattern for your first training, such as parallel lines or arrays of dots/squares, with variable size and pitch.

Access the software by using the username and password provided during your first training. As mentioned before, you can do this at any time, with or without operating also to the SEM LEO (just ignore the error). Go to Design () and Open your already prepared layout or click on New and use the GDS editor to design a new one.

Some useful information:

If you have a layout with significantly different feature sizes, place finer structures on a different layer than the bigger ones, in order to be able to pattern them with different doses.
Do not use layer 61, 62 and 63 for your features. These are connected to special functions inside Elphy.
Elphy's editor saves additional information such as dose modulation. During the import/export procedures some of them may be lost or modified. Always double check your layout after importing it.

Systems setup

When you are ready to pattern, log on the LEO SEM computer on LabManager and start the imaging software SmartSEM UIF as usual, and then start Remcon32, which can be found on the microscope's PC desktop as well. Select COM 6 from the dropdown menu, then right click and Open Port.
Move to the Raith pc and start ELPHY Quantum with your username and password (you will be assigned one during your first training).
If you did everything right, multiple lines of code will appear in the Remcon32 terminal and Elphy will start without prompting any error.

Mounting of chips or wafers into chamber

Mount samples in the dedicated Raith holder as shown in the picture, using the 3 clips available. Ensure that your sample is properly leveled, tightly kept in place by the clips, and is not obstructing the Faraday cup aperture. If the sample is insulating, you can use some conductive tape around exposure area to reduce charging.

Vent and open the SEM chamber, insert the holder on the LEO stage dovetail, close the chamber and pump down as usual.

Basic exposure

Set microscope main parameters

Once the vacuum is ready, start operating the microscope as in regular imaging. Be careful on where you are with your stage when activating the EHT, and always pay attention during stage navigation if the beam is not blanked. Any area which is imaged, is also going to be exposed, so you may risk destroying your pattern.

Set acceleration voltage, aperture and working distance according to your recipe.

Exposure parameters

In order to set the basic exposure parameters, go to the exposure tab and click on ???. Disable line, dot and curved elements.

Exposure parameters are connected by the following equation (visible in the pop-up window???), so they can't all be set at will at the same time. Also the current should read as the value previously measured and is not supposed to be modified.

Eq. dose=current*dwell/stepsize*linesize???

Select "equal step size"???, then input the desired values for step size and dose. Click on the little calculator button next to dwelling time - the software will compute the closest scan speed corresponding to that configuration. Click on the calculator next to dose - the software will update this value to a close one, to compensate for the non-continuous values available for the other parameters. This is your base dose, so remember to save it somewhere.

Unload and Shut off

Once everything is set and done, vent the chamber and unload your sample. Close Elphy on the Raith PC and Remcon32 on the LEO pc. Terminate your SEM LEO session as usual. The Raith PC remains operational even when LEO is locked.

Remember to place the Raith holder back in its box, and when logging out on Labmanager to fill the log book with "Raith session" = "Yes" and any relevant comment.

Obsolete

Pepare beam for writing

Before you start preparing your beam, a few recommendations:

It is recommended to move the stage (by joystick) instead of deflecting the beam (ctrl + tab); this to ensure that you work with an undeflected beam while preparing the beam for patterning and while patterning your GDS.
It is recommended not to rotate the scan by the 'scan' knob; this...

Measure beam current:
1. Click 'Stage Control/Positions/Faraday's cup', make sure the stage moves to the center of the Faraday's cup, increase the magnification to 100.000x or more
2. Toggle beam blanker to switch on beam
3. Make sure you operate at a working distance of 5 mm
4. Click 'XX' to measure beam current
Move the stage to a corner of your chip. With the joystick (or from the 'stage' tab in the SEM software), rotate the stage to align the chip
Adjust beam quality, i.e. focus, astigmatism, wobbling at a magnification of 100.000 x or more
Move to a new spot on the chip and switch the SEM to 'spot mode'; burn a spot in the resist (approximately 20s). Correct astigmatism and aperture alignment on that spot.
Burn a spot with a larger magnification and adjust beam quality again.
Burn a spot at a lower magnification to see that the spot is circular at this magnification

Stage adjustment

XY is stage coordinate system, UV is sample coordinate system:

Origin correction:
1. Click 'Adjustment/Adjust UV/Origin correction'
2. Move the stage to the lower left corner of the chip
3. Enter (U,V)=(0,0) and click 'adjust'
Angle correction:
1. Click 'Adjustment/Adjust UV/Angle Correction', make sure the system is in 'Global' mode
2. Turn on the crosshair (SmartSEM/View)
3. Set magnification to approximately 100x
4. turn off beam and click 'Label1/flash'-icon to move stage to the origin.
5. Click 'label1/pippette'-icon
6. Move stage to the lower right corner of the chip
7. click 'label2/pipette'-icon.
8. Click adjust: the button hereafter turns green