1. A method for producing a quantization functional device, comprising the steps of: (a) forming an etching protection film on a silicon substrate having a surface orientation of (001); (b) forming a first opening and a second opening in the etching protection film in one of a parallel direction and a perpendicular direction to a &lt;110&gt; crystal orientation of the silicon substrate, the first opening and the second opening being parallel to each other; (c) covering the second opening with an etchant resistive material; (d) forming a first groove in the silicon substrate at a position corresponding to the first opening by etching; (e) removing the etchant resistive material; (f) performing crystalline anisotropic etching to form the first groove into a shape having a substantially diamond-shaped cross section and a surface having a surface orientation of (111), and to form a second groove having a V-shaped cross section and a surface having a surface orientation of (111) in the silicon substrate at a position corresponding to the second opening, thereby forming a silicon thin plate sandwiched between the first groove and the second groove, surfaces of the silicon thin plate having a surface orientation of (111), and a distance between the surfaces of the silicon thin plate being sufficiently thin to allow the silicon thin plate to act as a quantum well; (g) forming a pair of tunneling barriers on the surfaces of the silicon thin plate; (h) forming a polysilicon layer on a surface of the silicon substrate so as to fill the first groove and the second groove, and doping an impurity having an identical conductivity with the conductivity of the silicon substrate into the polysilicon layer at a high density; and (i) patterning the polysilicon layer into a first electrode and a second electrode sandwiching the pair of tunneling barriers.