2001 年 52 巻 1 号 p. 125-129
Fusion bonding was conducted for anisotropically-etched Si wafers; the effects of surface morphology and thermally grown oxides on the wafers in relation to bondability were examined. Wafers with or without thermally grown oxides of a thickness of about 2μm were cleaned in RCA solutions to render their surfaces hydrophilic; they were then placed in face-to-face contact at room temperature, followed by in situ infrared inspection. After annealing at 1100°C in nitrogen for at least 1h, bond strength was measured using a four-point bending test. The wafers without thermally grown oxides provided better bonding results than those with oxides. After annealing, a bond strength of 10-20MPa was obtained, independent of the duration of annealing. Wafers with thermally grown oxides that were removed through immersion in an HF solution provided surface morphology and bonding results that were as good as those from polished wafers. Based on these results, a check valve structure was fabricated using anisotropic etching in a KOH solution and fusion bonding of wafers free of thermally grown oxides. Flow resistance for the forward flow of the fabricated check valve was one-three hundredths lower than that for the backward flow, indicating that the valve is highly one-directional.