Try the following and see if they help, 1. Add some He 2. Increase the chamber pressure 3. Make the wafer thermally contact very well to the base, i.e, using some thermal conductive glue. 4. Just for curiosity, for Si etch, why not try SF6? Good luck, Hongjun Zeng, PhD Microfabrication Application Laboratory(MAL) University of Illinois at Chicago 3014 ERF Building, 842 W. Taylor Street Chicago, IL 60607 Tel. 312-413-5889, Fax: 312-413-0447 -----Original Message----- From: Jason Milne Subject: [mems-talk] CF4 / O2 Silicon dry etch I'm doing some research into fabrication of silicon microlenses (~400 microns diameter, ~15 microns high) by photoresist reflow followed by transferring the resist profile into the silicon substrate with a dry etch using CF4 / O2 plasma. Everything is working fine, except that the surface of my lenses looks like the surface of the moon. They are covered with circular pits of different sizes, up to about 4 microns diameter and 100 nm deep. I have been unable to track down the source of this problem in the literature. If anyone knows of the origin of this surface damage, advice would be greatly appreciated. Attempting to isolate the origin of this damage, I have drawn the following conclusions that may help diagnose the problem: - Photoresist surface is fine before dry etch - Pits are occurring in the photoresist during the dry etch and are subsequently transferred into the silicon substrate - Damage is independent of RF power over the range 50W-200W and ICP power 300W-750W - Damage still occurs when temperature of resist surface does not exceed 85 degrees Celsius during dry etch - Damage still occurs if resist lenses are left for 24 hours before dry etch - If the resist lenses undergo a further high-temperature bake after reflow (5 mins bake, temperatures of 165, 185, 205 and 225 degrees), then the damage gets worse as the temperature of this bake is increased. My process parameters: AZ4562 resist Reflow at 145 degrees Celsius for 10 minutes CF4 conc. 20sccm O2 conc. 3sccm RIE powers: 50W, 100W, 200W ICP powers: 300W, 500W, 750W Pressure 10mTorr I also have photos of the silicon surface, if these would help shed light on the situation then please email me.