The integration level of dynamic random access memory (hereinafter referred to as “DRAM”) has increased year by year. Presently, a 64 gigabit DRAM cell having about a 70 nm design rule is expected to be manufactured by 2008, and a 1 terabit DRAM cell having about a 35 nm design rule is expected to be manufactured by 2014.
However, the conventional method of forming a layer, for example including an optical lithography technique and a chemical vapor deposition (hereinafter referred to as “CVD”) technique, is useful to manufacture a 64 gigabit DRAM cell or 1 terabit DRAM cell. As a result, research on an improved method of manufacturing a high density DRAM cell has been carried out intensively.
A new lithography technique using an electron beam (hereinafter referred to as “EB”) or X-ray has been developed as an alternative to the optical lithography technique, and an atomic layer deposition (ALD) technique has superseded the CVD technique. In addition, a semiconductor device is now feverishly under study, including a quantum dot of nanometric size, which can be applicable to a single electron gate.
A quantum dot can be formed using a focused ion beam (hereinafter referred to as “FIB”), or EB. The FIB or the EB can coercively put ions or atoms into a predetermined region of the semiconductor substrate and, advantageously, the FIB or the EB can easily control the size and the position of the quantum dot. However, the method of forming the quantum dot using the FIB or the EB has a low productivity and, thus, is not suitable for commercial applications.
The quantum dot can also be formed by nucleation of atoms. In particular, a non-crystalline layer having an amorphous substance is first formed, and then the non-crystalline layer is thermally processed to form a mono crystal. The method using the mono crystal provides a high productivity, but the size and the distribution of the quantum dot are hard to control.