Articles you may be interested inLow switching current flux-closed magnetoresistive random access memory J. Appl. Phys. 93, 7307 (2003); 10.1063/1.1557372Ultrahigh density vertical magnetoresistive random access memory (invited)High density submicron magnetoresistive random access memory (invited)The fabrication of magnetoresistive random access memory ͑MRAM͒ devices requires full characterization of the giant magnetoresistive ratio ͑GMR͒ permalloy films at the sub-0.5 m feature dimensions. Future memory arrays of the 1 and 4 Gb density require GMR bit cells of a 0.25 m and below in configurations which will require close proximity of cells. Since the cells are magnetic and act like tiny magnets, the switching field of a cell may be influenced by the polarization direction of the neighboring cell. This article describes the development of sub-0.5 m MRAM devices using current e-beam microfabrication techniques and the implementation of the latest chemically amplified deep ultraviolet resists. Etch processing is also discussed as well as the testing results for the 0.25 m arrays. Testing the GMR material at these dimensions consists of evaluating the single magnetic domain behavior and observing the effect of cell size on the magnetoresistance ratio. Array testing will consist of measuring switching field variations on a 0.25 m 5ϫ5 array to determine if there is field coupling with neighboring cells.
Full wafer charge coupled device interferometry is a new technique that can be used for in situ monitoring of plasma etching. The use of this technique to optimize an electron cyclotron resonance etch process for TaSiN and its application to x-ray mask fabrication are presented. Fine tuning of the etch process was performed by optimizing the microwave power and the collimating magnet current. Under optimized conditions, etch rate uniformity (3σ) across a 4 in. substrate was as low as 2%. The full wafer interferometer enables in situ uniformity measurements, thus minimizing process development time. The etch process has been used to successfully fabricate sub-0.25 μm x-ray masks.
The problem of polymer contamination in W trench etching is studied for fluorocarbon plasmas. Polymer contamination of narrow trenches has been observed on samples where isolated positive-relief structures (mesas) are clean. This effect is linked to sidewall sputtering by ions backscattered at low angles from the substrate: the sidewalls of a mesa are bombarded by reflected ions originating over a larger area of the substrate than the sidewalls of a trench. The presence of a blast of backscattered ions is confirmed (in an SF6/Br2 plasma) by images where sidewalls adjacent to large substrate areas etch isotropically while those in the shadow of an adjacent feature etch anisotropically. Finally, it is shown that ultrathin, durable polymer coatings which protect mesa sidewalls without contaminating nanometer-scale trenches can be formed in a magnetically enhanced, triode etching system using a CF4/O2 source gas: 40 nm wide, 300 nm deep trenches are shown.
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