Meihua Shen

Directional etch of magnetic and noble metals. II. Organic chemical vapor etch

Surface oxidation states of transition (Fe and Co) and noble (Pd and Pt) metals were tailored by controlled exposure to O2 plasmas, thereby enabling their removal by specific organic chemistries. Of all organic chemistries studied, formic acid was found to be the most effective in selectively removing the metal oxide layer in both the solution and vapor phase. The etch rates of Fe, Co, Pd, and Pt films, through an alternating plasma oxidation and formic acid vapor reaction process, were determined to be 4.2, 2.8, 1.2, and 0.5 nm/cycle, respectively. Oxidation by atomic oxygen was an isotropic process, leading to an isotropic etch profile by organic vapor. Oxidation by low energy and directional oxygen ions was an anisotropic process and thus results in an anisotropic etch profile by organic vapor. This is successfully demonstrated in the patterning of Co with a high selectivity over the TiN hardmask, while preserving the desired static magnetic characteristic of Co.

Directional etch of magnetic and noble metals. I. Role of surface oxidation states

An organic chemical etch process based on tailoring the surface oxidation state was found to be effective in realizing directional etch of magnetic and noble metals for their integration and application in magnetoresistive random access memory devices. Using Pt, a noble metal, as a test case, plasma treatments with sulfur- and oxygen-based chemistries were able to oxidize Pt0+ to Pt2+ and Pt4+, which can be effectively removed by selected organic chemistries. The most effective control of the surface oxidation states of Pt was achieved with an O2 plasma, which was then applied with similar effectiveness to other transition and noble metals. By quantifying the reaction rate, the oxidation of transition metals (Fe and Co) was shown to follow an inverse log rate law, while that of noble metals (Pd and Pt) follows a parabolic rate law. This work highlights the importance of the surface oxidation states of magnetic and noble metals in enabling directional etch by organic chemistry.

A New Etch Planarization Technology to Correct Non-Uniformity Post Chemical Mechanical Polishing

The introduction of 3-D structures and new materials for advanced logic devices at extremely fine feature size presents challenges for within-wafer and wafer-to-wafer thickness uniformity control that is critical for yield and performance. For conventional chemical mechanical polishing technology, the typical thin film uniformity across the whole wafer may not meet the desired variation target of 2-3 nm 3σ at some critical levels. Furthermore, wafer-to-wafer uniformity variation requires a wafer by wafer approach to uniformity correction. In this paper, a novel etch planarization technology is presented that combines a conventional production-proven etch process that is temperature sensitive with an inductively coupled plasma reactor equipped with a novel electrostatic chuck that provides die level thermal control. Improved process control enables cost effective uniformity improvements in excess of 85%.

Etch planarization - A new approach to correct non-uniformity post chemical mechanical polishing

The introduction of 3D devices and new materials at sub 28 nm nodes presents challenges for within-wafer and wafer-to-wafer CMP thickness uniformity control that are critical for device yield and performance. Upon CMP the typical thin film uniformity across the whole wafer is unable to meet the target of less than 2 nm 3σ variation. Furthermore, wafer-to-wafer uniformity variation requires a wafer by wafer approach to uniformity correction. In this work, a novel etch planarization approach is presented that combines a conventional production-proven etch process that is temperature sensitive on an inductively coupled plasma reactor with die level thermal controlled electrostatic chuck (ESC). Improved process control enables cost effective uniformity improvements in excess of 85%. In addition, the approach provides wafer-to-wafer tuning capabilities.