COMELEC C-30-S Parylene Coating System

Comelec C-30-S Parylene deposition system

Introduction Parylene is a polymere deposited at room temperature in a vacuum chamber (few µb). Parylene coating is perfectly conformal. Parylene is a pinhole free layer resistant to HF, KOH and solvents. Its thickness can vary from few tens of nm to tens of μm with a deposition rate of few μm/hour. Parylene is easy to dry etch (istropic or anisotropic).

Parylene can be use as a:

• Protective or support layer for sensitive device,

• Sacrificial layer with Al or Si device,

• Device layer with PR, SiO2 or Si as a sacrificial layer.

Basic of deposition Parylene raw material is a solid dimmer. The system works under a primary vacuum (few μb). The dimmer is heated at about 150°C and changes to a vapor phase. It diffuses to Pyrolysis chamber at 670°C and is dissociated in a monomer. The monomer diffuses to the room

temperature or slightly heated (80°C) process chamber, and condensates to fabricate Parylene layer. Before being pump, residual monomers are trapped in a cryogenic device.

The layer thickness depends on the Parylene solid load placed in the vaporization boat. Total surface and arrangement in the processing chamber influence the thickness and uniformity. At 100mm Silicon wafer scale layer uniformity is less than 1%.

Parylene coating principle (Courtesy of www.comelec.ch).

Parylene front panel, 10 slots holder and processing chamber

Parylene Load Estimation Parylene load (g) 0.20 7.00 11.00 Avg. thickness 62nm 2.09µm 3.15µm Table: Processes performed with 3 Si wafers (100mm) loaded in lower, medium and higher slots.

How to proceed to use the system 1. Idle mode

- Chamber is pumped: vacuum chamber and pump pressure should be few µbar, - LN2 trap is clean, empty and under vacuum, - Substrate holder is empty and under vacuum, - Parylene container is empty and under vacuum, - Zone 1 (vaporization) and zone 2 (pyrolysis) are off,

2. Make a coating

- Before starting: oo Switch on zone 2. It takes 1 hour to get it ready. You can switch it on

automatically with a timer. “Please fill process sheet: Time, pressures” “Please fill process sheet: Time, pressures”o Switch on the balance,

- Chamber venting: o Close the valve chamber: “vanne chambre” light ON becomes OFF. It takes

30s to get it closed, o Vent the chamber: “vanne air” light OFF becomes ON. It takes approximately

1min to vent, - Wafers/samples loading:

o Put on a pair of gloves, o Open the chamber lid, o Switch of venting, press “vanne air”, o Get the holder out and put it on the table, o Place wafers on the holder shelves (10slots), o Put back the holder in the chamber. Holder base must be properly positioned to

rotate it later, o Press “rotate” and check if it goes well, o Close the lid,

- Parylene load (keep the gloves): o Open the load door to get the Parylene container out, o Fit a new aluminium protection, o Move everything on Mettler-Toledo balance, adjust the zero (press tare), and

fill with the appropriate Parylene quantity (see our table), o Move the filled container back to the loading room, o Close the door,

- Pump the chamber: o 3 checks before pumping:

LN2 trap placed, Chamber lid closed, And Parylene loading door closed,

o Press “vanne chamber” to pump the chamber, “Please fill process sheet: Time” “Please fill process sheet: Time”o Press F4 to put the lot number: “quantity of Parylene”g-run number, for

example 7g-004 (7g Parylene load and run number 4), press F11, o Once vacuum is below 20µbar in the chamber, it takes between 5 to 15min

(function of the state of the machine), it is time to fill the LN2 trap, “Please fill process sheet: Time, pressures”

“Please fillprocess sheet: Time, pressures”

- LN2 trap filling: o Put on safety glasses and LN2 gloves, o Fill the trap using the LN2 dewaer by applying some pressure on top (open the

LN2 line + apply pressure with the manometer), o Once LN2 start spilling outside the trap, drop the flow by screwing the valve

until the trap is full (10cm below the top). This operation takes about 5min. o If necessary, complete the filling with the thermal can near the system, o Put the LN2 stopper - height measurement plug, o Check on the C-30-S display if height is fine (90%),

- Start deposition:

o Once the chamber pressure is 5-6µbar (pump pressure always lower) press “zone 1” to start Parylene dimmer vaporisation, “Please fill process sheet: Time, pressures”

“Please fill process sheet:Time, pressures”

o Press F1 to monitor pressure chamber, - End of deposition:

o Once pressure is back to 5-6µbar deposition is finished. There is no Parylene dimmer left in the system. “Please fill process sheet: Time, pressures” “Please fill process sheet: Time, pressures”

o Switch off “zone 1” and WAIT 10MIN BEFORE VENTING TO CLEAR EVERYTHING in the system, “Please fill process sheet: Time, pressures” “Please fill process sheet: Time, pressures”

- Chamber venting: o Close the valve chamber: “vanne chambre” light ON becomes OFF. It takes

30s to get it closed. o Vent the chamber: “vanne air” light OFF becomes ON. It takes approximately

1min to vent. - Wafers/samples unloading:

o Put on a pair of gloves, o Open the chamber lid, o Switch of venting, press “vanne air”, switch off “rotation”, o Get the holder out and put it on the table, o Take out wafers from,

- LN2 trap cleaning: o Put on safety glasses and LN2 gloves, o Make ready an open thermal bottle, o Pull out the trap and empty the LN2 in the thermal bottle, o Take off glasses and LN2 gloves, o Go to the washbasin and scrub the outside of the trap, o Dry it and put back after O’ring checking,

- Chamber lid and O’ring cleaning: o Below the lid Parylene film is easy to delaminated, o Remove the O’ring and clear parylene on the top surface. You can use a blade

to cut it. o Clean sealing surfaces with some IPA, o Wipe the O’ring, put some vacuum grease and fit it in the groove,

- Chamber pumping: o Put back the holder in the chamber. o Close the lid. o 3 checks before pumping:

LN2 trap placed, Chamber lid closed,

And Parylene loading door closed, o Press “vanne chamber” to pump the chamber, “Please fill process sheet: Time” “Please fill process sheet: Time”

3. Leave the system in Idle mode

o If no more deposition are planed, switch off zone 2 o System in Idle mode:

Chamber is pumped: vacuum chamber and pump pressure should be few µbar,

LN2 trap is clean, empty and under vacuum, Substrate holder is empty and under vacuum, Parylene container is empty and under vacuum, Zone 1 (vaporization) and zone 2 (pyrolysis) are off

Photos Gallery

Fig. 1: Si wafer coated with 11.5um Parylene (0.5% uniformity).

Fig. 2: Parylene conformal coating in deep Si cavities. Parylene is delaminated after sample cleavage.

Fig. 3: Parylene isotropic etching to release aSi structures.

Fig. 4: Anisotropic etching of Parylene with aSi mask.