- Power: 100 W
- Pressure: 100 mTorr
- Gases: 3.1 SCCM 02, 25 SCCM CF4
- Etch Rate: 0.15 microns/min.
- Selectivity: 1.3
Detail Process Parameter
- Gas Mixture
The best ratio for selectivity if Si vs. photoresist is of O2:CF4 is 11%. If another selectivity is desired for some reason, refer to graph one for various selectivities vs. O2%. This data was obtained using 100W of RF power at %0 mTORR in the RIE, but the trend holds fore all 100 mTORR and higher power rates as well.
- Chamber Pressure
The best chamber pressure we have found so far is 100 mTORR. The RIE has several pressure gauges, and they all give slightly different readings from one another. This data was compiled using the Baratron etching gauge, labeled on the front of the machine. Because of the sensitivity of this gauge, it should not be exposed to a full atmosphere's pressure, so close the shutoff valve to the etching gauge before venting the chamber to atmospheric pressure. From our admittedly incomplete characterization of the RIE, this pressure seems to serve best for both maximizing selectivity and anisotropy of silicon etch. Below is a table of selectivity at different pressures.
- Power Setting
The power setting determines how much power the RF supply outputs to the chamber. Etch rate increases with power, but tapers off logarithmically as the power increases. The RF supply has the capability of delivering up to 600 watts forward power, but we have found that the photoresist starts to char at settings as low as 250 watts. More than 300 watts forward power should not be used on the machine. Generally, we have found that a setting of 100 watts forward power maximizes selectivity of etching.
- Using the Spreadsheet Data
Equipment specific data has been collected in an excel spreadsheet: DOWNLOAD FILE
There are five worksheets on the spreadsheet:
- Mix 100W: selectivity and etch rate data using different mixtures of O2 and CF4 process gases at 100W RF power
- Mix 200W: selectivity and etch rate data using different mixtures of O2 and CF4 process gases at 200W RF power
- Pressure Spread: selectivity and etch rate data for different chamber pressures
- Power Spread @ 50 mTORR: selectivity and etch rate data at different power settings, at 50 mTORR chamber pressure
- Power Spread @ 100 mTORR: selectivity and etch rate data at different power settings, at 100 mTORR chamber pressure