Bonding energy of silicon and sapphire wafers at elevated temperatures of joining

The hydrophilicity of surfaces and the bonding energy of silicon and sapphire wafers at the temperature of joining 50$^{\circ}$C are studied. It is established that heating of the Si and Al$_2$O$_3$ wafers to 50$^{\circ}$C is accompanied by an increase in the degree of hydrophilicity of the wafer surfaces. The effect is attributed to improvement in the surface purity due to the desorption of impurity atoms into vacuum and to an increase in the density of dangling bonds. It is found that the bonding energy of silicon and sapphire wafers joined at a temperature of 50$^{\circ}$C and upon further heating in the range 100–250$^{\circ}$C is higher compared to the bonding energy of wafers joined at room temperature. The activation energy of the growth of the bonding energy is determined. It is found that this activation energy is 0.57 eV.