We have formed Sb nanocrystals in thin, thermally grown SiO2 layers using low-energy ion implantation which was followed by thermal annealing. These Sb nanocrystals showed good uniformity with respect to size and position. Both the narrow as-implanted profile and the compressive strain that exists near the SiO2/Si interface are considered to contribute to the uniformity. We found that it was possible to control the size of the Sb nanocrystal by changing the dose of the implanted Sb, The I-V characteristics of the diodes which had Sb nanocrystals with an average diameter of 3.3 nm showed good reproducibility. Moreover, these diodes showed a Coulomb blockade region around 0 V and a Coulomb staircase at 4.2 K. Identical I-V characteristics were obtained for all the samples measured, indicating an excellent reproducibility. Almost the same Coulomb blockade region as that at 4.2 K was observed up to a temperature as high as 100 K even for a diode which had larger Sb nanocrystals (with an average diameter of 5.6 nm). The technique introduced here offers the possibility of developing practical Si-based single-electron devices.