Patterned Garnet Films on Substrates with Ion-Beam Bombarded Micropatterns
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Mat. Res. Soc. Symp. Proc. Vol. 517 01998 Materials Research Society
plasma energy employed was 0. 2keV, suggesting that even such small energy (compared to other ion beam bombardment methods) can affect the conditions for growing single crystal films of bismuth substituted YIG. [6] However, the plasma yielded by conventional sputtering exhibited nonuniformity, which led to irregularity of the substrate surface. Therefore, the method is not appropriate for controlled surface modification, although no detailed observation of the surface state was performed. We employed an ion-beam etching technique for the surface modification of a gadolinium gallium garnet (GGG) substrate instead of rf-sputtering. Ion-beam etching can remove atoms from the surface of a solid by bombardment with a collimated beam of ions. Since ion-beam etching takes place external to the ion discharge chamber, substrates are not subjected to a plasma environment. In addition, ion energy and ion flux density may be independently controlled, and substrate orientation to the ion beam may be varied. Disordered bonding atoms exist on the surface of the substrate and residual damage exists in the surface depth. We calculated the damaged layer depth on the order of few angstroms to tens angstroms into the GGG substrate irradiated by 0.2keV argon ion bombardment using transport-of-ions-in-matter (TRIM) simulator. [8] Furthermore, the residual damage inside of the layer near the surface can be removed by heating when growing the film. We used a Kauffman type ion-beam mil with a 3cm-diameter ion gun and Ar as the bombardment ion. The etching was performed at 2.6x10 2- Pa. The ion-beam bombardment energy and current were varied from 0.2 to lkeV and from 10 to 25mA (current density ranging from 1.4 to 3.5mA/cm 2), respectively. 2.2. Film deposition of cerium substituted yttrium iron garnet by magnetron sputtering The apparatus for growing in-situ epitaxial films influences various properties of the films. Here we employed rf-magnetron sputtering in an ultrahigh vacuum (UHV) chamber originally designed for the molecular beam epitaxy. [9] Energetic particle bombardment of the growing film from an rf-magnetron plasma is negligible by comparison with an rf-diode plasma. In rf-diode sputtering a growing film is exposed to ion bombardment even at floating potential. Film perfection is impaired by particles arising from disintegration of target surface. The background vacuum in the chamber was two-orders of magnitude lower than conventionally used in sputtering: 10 6Pa. A sintered ceramic target was used with the stoichiometric composition of Ce1 Y2Fe5 O12 . However, the oxygen content in the deposited film was probably decreased due to the instability of the cerium trivalent ion. A lamp heater was employed to heat the substrate instead of a resistive heater to avoid contamination. The deposition 2was carried out under the following conditions: argon atmosphere mixed with oxygen of 2.6xl0 Pa, an rf power density of 2.5W/cm , an oxygen flow rate of 0. 5ccm, a substra
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