A shallow junction that previously would require the use of a low-energy ion implanter can be directly formed by high-energy or middle-energy ion implanters such that the manufacturer need not purchase a new low-energy ion implanter. In one embodiment, an ion-implantation method for forming a shallow junction comprises providing a semiconductor substrate including at least one transistor structure. During ion implantation to form a shallow junction, a buffer layer is formed on the implantation region. The buffer layer has a predetermined thickness. Charged ions are implanted into the implantation region through the buffer layer by an energy provided by a middle-energy ion implanter, and the buffer layer is removed. The buffer layer is used for blocking the amount of the charged ions that will be implanted into the implantation region so as to form a shallow junction that would require a low-energy ion implanter without the buffer layer.