Data Storage Systems Center

The fabrication of magnetic based structures, including MRAM and patterned media, typically requires that etching be performed on one or more magnetic films. Traditionally, ion milling has been used for this process. However, the purely physical nature of the milling process produces several drawbacks, which can include redeposition of etched material, shadowing of the ion beam, poor etch selectivity, cross-wafer non-uniformity, and etch induced damage. Given these drawbacks, researchers have naturally searched for alternative etching methods. One such method with a great deal of potential is known as reactive ion etching (RIE). Already adopted by the semiconductor industry, RIE combines both physical and chemical etching processes to uniformly control the etch profile across the wafer. The inclusion of the chemical etch component helps to increase selectivity, decrease redeposition and shadowing, and to minimize etch damage from physical bombardment by forming volatile compounds that are easily removed from the sample. We have chosen to pursue methanol (CH3OH) as the reactive etching gas due to its ability to etch various magnetic and non-magnetic films down to nanoscale dimensions. In addition, methanol can have very good selectivity over a variety of mask materials, including Ta, TaNx, Ti, SiNx, and various multilayer combinations of these materials. Through the use of a parallel plate RIE system, we have successfully used methanol to etch both isolated and dense discrete tracks into commercially available perpendicular recording media with groove widths as narrow as 20nm, and we have been able to fabricate nanoscale pillars and rings in materials, such as NiFe. More recently, we have obtained an inductively coupled plasma (ICP) RIE system to be used for methanol etching. In the ICP configuration ion bombardment and plasma density can be controlled separately, unlike the parallel plate setup where they work in synergy. Therefore, it is possible to produce faster etching rates, better selectivity, and even less ion induced etching damage. All of these factors will aide in the etching of even smaller features with higher aspect ratios than those obtained in the parallel plate setup.

The fabrication of magnetic based structures, including MRAM or patterned media, typically requires that etching be performed on one or more magnetic films. Traditionally, ion milling has been used for this process. However, the purely physical nature of the milling process produces several drawbacks, which can include redeposition of etched material, shadowing of the ion beam, poor etch selectivity, cross-wafer non-uniformity, and etch induced damage. Given these drawbacks, researchers have naturally searched for alternative etching methods. One such method with a great deal of potential is known as reactive ion etching (RIE). Already adopted by the semiconductor industry, RIE combines both physical and chemical etching processes to uniformly control the etch profile across the wafer. The inclusion of the chemical etch component helps to increase selectivity, decrease redeposition and shadowing, and to minimize etch damage from physical bombardment by forming volatile compounds that are easily removed from the sample. In order to produce volatile compounds with magnetic materials, many researchers have concentrated on etch chemistries that include gases, such as Cl2 or NH3. However, these highly toxic, corrosive materials require special tooling and post etch treatments to remove corrosive residue that may damage magnetic films. On the other hand, methanol gas (CH3OH) requires no special tooling and produces no corrosive residue. Therefore, we have chosen to pursue methanol etching of magnetic devices and magnetic recording media using a standard parallel plate RIE process. We have demonstrated that various magnetic films, as well as some non-magnetic films can be etched to nanoscale dimensions with very good selectivity over a variety of mask materials, including Ta, TaN, Ti, SiNx, and various multilayer combinations of these materials. Consequently, we have been able to successfully etch both isolated and dense discrete tracks of varying linewidth into commercially available perpendicular recording media, and we have been able to fabricate nanoscale pillars and rings in materials, such as NiFe.