Competitive Oxidation During Buried Oxide Formation Using Separation by Plasma Implantation of Oxygen (Spimox)
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Abstract We have recently demonstrated a new implantation technique called SPIMOX (separation by plasma implantation of oxygen) to synthesize silicon-on-insulator structures using plasma immersion ion implantation (PIII) process. The implantation is performed by applying a large negative bias to a Si wafer immersed in an oxygen plasma created by an ECR source. Since the technique has no mass analysis, coexistence of O and 02, ions in oxygen plasma can cause a non-Gaussian profile of the as-implanted oxygen distribution. We observed that during postimplantation annealing, the ripening process of the oxide precipitates depends on depth and concentration of the oxygen peaks. In addition, implanted oxygen can migrate towards the Si surface during annealing, preventing a continuous buried oxide layer formation. In this paper, we report our observation on the effect of the implantation profile on the competitions between internal oxidation at different depths and between internal and surface oxidation processes. With an additional He implantation, we demonstrate that the nucleation of oxide precipitation can be enhanced. Introduction
Silicon-on-insulator (SOI) structure has many attractive advantages for high packing density and high performance IC devices[l]. In recent years, thin SIMOX[2] which is characterized by the top silicon layer being thin enough for fully depleted devices has attracted attention. Different from conventional thick SIMOX, the continuous buried oxide (BOX) layer in thin SIMOX process is not achieved during the implantation stage of the process. It forms via a ripening process of the oxide precipitates at the post-implantation annealing step during which larger precipitates grow on expense of dissolving smaller ones at high temperature. The growing precipitates will eventually coalesce to form a continuous buried oxide layer. It is obvious that the location of the nucleation sites and the post-implantation annealing sequence are extremely important for the quality of the buried oxide and top silicon layers formed. Separation by plasma implantation of oxygen (SPIMOX)[3] is a method that can be used to form buried oxide layers in silicon wafers for SOI (silicon-on-insulator) applications. The method is based upon a combination of the separation by implantation of oxygen (SIMOX)[1] process and the plasma immersion ion implantation (PIII)[4] process, and is motivated by the desire to reduce the manufacturing cost of SIMOX wafers for SOI devices by reducing the implantation time. According to projection, a two order-of-magnitude reduction in implantation time is possible. The SPIMOX process is achieved by applying a large negative bias voltage to a Si wafer immersed in an oxygen plasma so that the ions in the plasma are 385 Mat. Res. Soc. Symp. Proc. Vol. 388 0 19 9 5 Materials Research Society
accelerated across the plasma sheath layer and implanted into the entire wafer surface at the same time. A large implantation current is therefore achievable with a tolerable current density. The most attracti
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