Hi Nirmal, That's a very slow spin speed, so it's going to be tough to get a flat surface. My suggestion is to spin at 800 rpm and postpone the pre-bake. Instead, place the wafer on a flat level surface for a day or two (cover it so that it stays clean) to allow the unbaked resist to self level. I don't know if it will meet your requirements for flatness, but it should be better than spinning only. Best, Joe Grogan Quoting Nirmal punjabi: > Hi, > > I need a thickness of around 400um of SU-8, i am spin coating SU-8 2100 at > 800rpm for 60 sec. > > But the final structure formed has uneven surface. > > Can anyone help me on this matter? > > Thank you. > > Nirmal. -- Joseph M. Grogan Doctoral Candidate Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania 220 South 33rd street Room 229, Towne Building Philadelphia, PA 19104 Lab Phone: 215-898-1380