Specific Process Knowledge/Etch/HF Vapour Phase Etch

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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 vapors easily diffuse into "hidden spaces" making e.g. long undercuts, membrane and resonator release etches feasible.

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...

1. 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
2. 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
3. Adjust beam quality, i.e. focus, astigmatism, wobbling at a magnification of 100.000 x or more
4. 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.
5. Burn a spot with a larger magnification and adjust beam quality again.
6. 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:

1. 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'
2. 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