Amorphous Si/SiO2 superlattices have been deposited on glass substrates using two-target alternation magnetron sputtering technique. The samples are characterized using transmission electron microscope and low-angle X-ray reflectance techniques. The results indicate that most of the regions in Si layers consist of amorphous phase in the superlattices, while the regular structure appears in some local regions rarely. The thicknesses of Si layers are in a range from 18 to 3.2nm and the thickness of SiO2 layer is 4.0nm in all cases. The samples are systematically studied using absorption, photoluminescence (PL) and Raman spectroscopy techniques. The absorption edge positions and PL peaks shift towards shorter wavelengths while Raman spectra show broader peaks with decreasing Si layer thickness. The results are mainly attributed to the quantum confinement effects.