MDA-0120 Microtrenching RIE as a Means of Etching Sidewall-Free MTJs
Original Publication Date: 2007-Apr-05
Included in the Prior Art Database: 2007-Apr-05
Reactive ion etching of materials that do not form readily volatile compounds generally results in the formation of "fences," "veils," or "sidewall redepositon" of the material as it is sputtered from the field onto the sides of protruding structures nearby. This disclosure describes a method by which these harmful fences can be avoided. By adjusting the angle of incoming ions during the etch, one can achieve higher sputter yield of the material on the sidewalls of protruding structures. This higher sputter yield effectively prevents the fences from forming.
MDA-0120 Microtrenching RIE as a Means of Etching Sidewall -Free MTJs
Many materials used in research, development, and production of modern electronic devices present problems because they are not readily etched with reactive ion etching (RIE) techniques. These techniques rely in part on a chemical component to the etch (creating a volatile molecule from the to-be-etched material), and in part on a physical component (additional energy imparted to the molecule by incoming ions, thus enhancing the evaporation of the material). A suitable balance between chemical and physical components can yield ideally structured features with, for example, very sharp sidewalls. However, for many of today's materials of interest, the chemical component of etching is severely lacking because these materials do not easily form compounds that are volatile at reasonable processing temperatures. When etching these materials, the physical component (sputtering) dominates, and this tends to allow redeposition of the sputtered material on the surfaces being etched. This is a particularly harsh problem when features with significant protuberance exist, effectively catching the sputtered material on the sidewalls of the protuberance. On such sidewalls, sputter yields are greatly decreased because of an infavorable angle of incoming (sputtering) ions relative to the the material on the sidewall.
Common methods for eliminating this sidewall redeposition include: a post-etch wet chemical cleaning step that is nondirectional, and attempting to taper the edges of the protuberances such that they offer better sputter yields for material deposited thereon. Drawbacks to these methods include: wet chemical damage to sensitive layers that may be exposed during the etch, and a difficulty in reducing device dimensions due to additional space required to allow for tapered feature edges.
This disclosure describes an alternative method for eliminating the harmful formation of fences on the sidewalls of protruding structures during ion etching, and can be used both in reactive ion etching or in ion milling (or ion beam etching). The essence of the idea is to modify the angle of incoming (physically sputtering) ions such that the sputter yield on the sidewa...