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We present a method to form a patterned template having a dense array of subnanometer scale pits that is useful for numerous applications that require significant size reduction. The polystyrene-polymethylmethacrylate diblock copolymer nanopatterned sample has been used in order to form a hexagonal symmetry as a starting scaffold. The ordered copolymer pattern is then transferred to the oxide layer to form a hard mask for subsequent anisotropic silicon wet-etching process. With a controlled wet etching, we obtained inverted pyramidal pits on a silicon substrate of which the tips can be a few or even a single nanometer in its lateral dimension. The most common phase change material Ge2Sb2 Te5 (GST225) was deposited on this substrate and isolated within the pits using chemical mechanical polishing approach, followed by X-ray photoelectron spectroscopy elemental analysis.