Fin Field Effect Transistors (FinFETs) are becoming increasingly attractive due to their good control of short channel effects. FIG. 1 is a perspective view schematically showing a FinFET by way of example. As shown in FIG. 1, the FinFET comprises a bulk Si substrate 100, a fin 101 formed on the bulk Si substrate 100, a gate stack 102 crossing over the fin 101 and including, for example, a gate dielectric layer and a gate electrode layer (not shown), and an isolation layer (e.g., SiO2) 103. In this FinFET, under the control of the gate electrode, conductive channels are formed in the fin 101, and specifically, in three side surfaces (i.e., a left side surface, a right side surface and a top side surface as shown in the figure) of the fin 101. That is, a portion of the fin 101 under the gate electrode serves as a channel region, and source and drain regions are located at either sides of the channel region, respectively.
In the example shown in FIG. 1, the FinFET is formed on the bulk semiconductor substrate. Alternatively, a FinFET can be formed on other types of substrate, such as a Semiconductor On Insulator (SOI) substrate. Furthermore, the FinFET shown in FIG. 1 has the channel formed in all the three side surfaces of the fin 101, and thus is referred to as a 3-gate FinFET. On the other hand, a 2-gate FinFET can be formed by, for example, providing an isolation layer (e.g., nitride) between the top surface of the fin 101 and the gate stack 102, in which case the top surface of the fin 101 will not be subject to the control of the gate electrode and thus will have no channel formed therein.
However, as shown in FIG. 1, the bottom portion of the fin is surrounded by the isolation layer of SiO2 103, and thus cannot be effectively controlled by the gate electrode. Thus, there may be a current path between the source and drain regions through the bottom portion of the fin even in the off state, resulting in current leakage.
Therefore, there is a need for a semiconductor device and a method for manufacturing the same, by which it is possible to effectively reduce the current leakage at the bottom portion of the fin.