Consideration of target platen materials in plasma immersion ion implantation

In plasma immersion ion implantation (PIII), ions are acclerated from the overlying plasma by applying a negative voltage to the sample stage. Hence, ions impinge into not only the sample but also all exposed area of the sample platen. In most cases, the exposed sample platen area is larger than that of the sample (e.g. a silicon wafer) and constitutes the main load of the power modulator. Our theoretical simulation reveals that in typical PIII conditions, over 70% of the ions bombard the side and bottom of the sample platen. The materials that make up the sample platen surface thus have a critical influence on the secondary electron emission, sample heating, and amount of sputtered contaminants. The secondary electrons affect the electrical efficiency, design of the modulator, as well as x-ray production and the subsequent protection. Sputtering of the target platen releases metallic and other ions into the plasma that can contaminate the samples. The choice of a compatible material is thus critical in processes such as SPIMOX (separation by plasma implantation of oxygen). The target platen heat capacity affects the sample temperature that is critical in elevated-temperature or room-temperature processes such as high-frequency, low-voltage PIII and hydrogen PIII/ion-cut. In this paper, we present results acquired from theoretical and experimental investigations on the target materials selection and the influence on the treatment results.