We prepared SOI (silicon-on-insulator) wafer pairs of 2000 Å -SiO 2 /Si(100) and 560 Å-Si 3 N 4 /Si(100) by CFA (Conventional electric Furnace Annealing), RTA (Rapid Thermal Annealing), and FLA (Fast Linear Annealing) at different annealing temperatures for each annealing process. We measured the bonding area and the bonding strength for the respective processes. It was demonstrated that the measured bonding area was close to 100 % above 450 o C for RTA, and 400 o C for CFA. The maximum bond strength of the SiO 2 / Si 3 N 4 wafer pair was 2344, 2300, and 195 mJ/m 2 for CFA, FLA, and RTA, respectively. We clearly demonstrated that the FLA method is far superior in producing high-quality directly bonded Si wafer pairs with SiO 2 and Si 3 N 4 films compared to the CFA and RTA methods.
Magnetic tunnel junctions (MTJ) with the tunnel barrier oxidized in two steps with plasma were fabricated to obtain a structurally uniform AlO x insulator. Plasma oxidation of 10 Å-thick Al layer for 5~20 sec formed the initial oxide barrier on top of which a second oxide layer was deposited by oxidizing 13 Å-thick Al for 120 sec. The doubly oxidized junctions exhibited a magnetoresistance (MR) ratio of 27~31 % depending on the oxidation period of the initial oxide layer while only 24 % was obtained for the junction deposited in one-step oxidation with a similar stack configuration. The junction resistance of the MTJ increased monotonically with oxidation time while minimal deterioration of the MR ratio was observed when oxidation time increased from 5 sec to 20 sec. Transmission electron microscopy of the junctions also confirmed that the AlO x thickness was thinner for the doubly oxidized junctions compared to the singly oxidized MTJ. X-ray photoelectron spectroscopy of the double junction also strongly suggested that the initial oxide layer prevents over-oxidation of the bottom electrode. Our results suggest that the AlO x oxidized in two steps produces improved junction performance as well as a wider processing window.
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