The sidewall scallops come from the chemical nature of the Bosch process. Specifically a Bosch process involves anisotropic etching (SF6), followed by a placement of a passivation layer on all surfaces (from C4F8), and repeat. Some choose to add an oxygen plasma step to help removing the polymer that deposited on the etch surface. Note that there is no such thing as an RIE that is just chemical or just physical...every RIE process is a combination of both, hence the name Reactive Ion Etching. If it is just physical it is called Ion Milling and if it is just chemical then your wasting power creating a plasma. The reason why the Bosch process is used is that no process is 100% anisotropic. For various reasons (ion bowing as an example) the etch part of the Bosch process (or any plasma etch left long enough for that matter) will cause a sort of balloon etch. Once the passivation layer is placed on the walls, this balloon hole will not open up any more, instead the bottom of the hole will go deeper during the next etch phase and create a the balloon feature below it. It is hard to explain without drawings but most any MEMS textbook will explain it in greater detail. Also a quick search on google and I found this page which has some good drawings to explain scalloping and notching http://cmi.epfl.ch/etch/Talk_Cyrille_CMI2004.pdf. So as to why the solutions I suggested: First off higher substrate power will pull the ions down more vertically, giving them better directionality and less of the balloon effect. Too much however and you start getting the balloon back since the ions will just start milling and shooting the byproducts back out at random directions. With higher power also comes more speed, more roughness at the bottom of the pit, and it is harder to control etch depth. As for the shorter cycles, it will make smaller balloons before moving deeper. The smaller the balloon, the smaller the scallops. You will also get a much slower etch and probably use up more of your reactant gas. Hope this description helped. Nicolas "Nik" Duarte Penn State University PhD Student under Dr Srinivas Tadigadapa At 11:12 AM +0100 9/11/06, K A Chan wrote: >Nik, >Can you explain why higher substrate power and shorter cycles could >reduce the scallops? >What chemistries have been used in Bosch process? Is it a pure >chemical etch or a combination of chemical + physical etch with high >energetic bombardment of ions using high substrate power?