A first semiconductor region and a second semiconductor region separated by a shallow trench isolation region are formed in a semiconductor substrate. A photoresist is applied and patterned so that the first semiconductor region is exposed, while the second semiconductor region is covered. Depending on the setting of parameters for the location of an edge of the patterned photoresist, the slope of sidewalls of the photoresist, the thickness of the photoresist, and the direction of ion implantation, ions may, or may not, be implanted into the entirety of the surface portion of the first semiconductor region by shading or non-shading of the first semiconductor region. The semiconductor substrate may further comprise a third semiconductor region into which the dopants are implanted irrespective of the shading or non-shading of the first semiconductor region. The selection of shading or non-shading may be changed from substrate to substrate in manufacturing.