After being treated with clean wafer, {TAIL ~ about 1 μm thick thermal oxidation films 13a}, 13b are formed on the bonding surfaces of {HEAD ~ these substrates} by, for example, thermal oxidation or CVD in a clean atmosphere of below Class 1 as shown in FIG 3A 
After being treated with clean wafer , { TAIL ~ about 1 μm thick thermal oxidation films 13a } , 13b are formed on the bonding surfaces of { HEAD ~ these substrates } by , for example , thermal oxidation or CVD in a clean atmosphere of below Class 1 as shown in FIG 3A
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