Alternatively, in another embodiment as shown in FIG. 3A′, the substrate 100 is formed by providing a bulk silicon substrate 102A, forming a stop layer 104 on the bulk silicon substrate 102A and then forming a silicon layer 102B on the stop layer 104. The stop layer 104 is sandwiched between the bulk silicon substrate 102A and the silicon layer 102B (i.e., embedded in the bulk silicon substrate 102). The bulk silicon substrate 102 in FIGS. 2A & 3A is considered as comparable or equivalent to the bulk silicon substrate 102A and the silicon layer 102B in FIG. 3A′. In some embodiments, the material of the stop layer 104 includes SiGeOx, SiGe, SiOx, SiP, SiPOx, or the combination thereof. In some embodiments, the stop layer 104 has a thickness ranging from 1 nm to 50 nm, for example. In one embodiment, the stop layer 104 is formed by atomic layer deposition (ALD) or any other suitable deposition process, for example. The thickness of the silicon layer 102B may be determined depending on the requirements of the design.