Investigation of silicon on insulator fabricated by two-step O+ implantation

Abstract

In this paper, we investigated the dose window of forming a continuous buried oxide (BOX) layer by single implantation at the implantation energy of 200 keV. Then, an improved two-step implantation process with second implantation dose of 3×10 15 cm −2 was developed to fabricate high quality separation by implanted oxygen (SIMOX) silicon on insulator (SOI) wafers. Compared with traditional single implantation, the implantation dose is reduced by 18.2%. In addition, the thickness and uniformity of the BOX layers were evaluated by spectroscopic ellipsometry. Defect-free top Si as well as atomic-scale sharp top Si/buried oxide interfaces were observed by transmission electron microscopy, indicating a high crystal quality and a perfect structure of the SOI fabricated by two step implantation. The top Si/BOX interface morphology of the SOI wafers fabricated by single or two-step implantation was also investigated by atomic force microscopy. silicon on insulator, interface morphology, dose window, separation by implanted oxygen Citation: Wei X, Xue Z Y, Wu A M, et al. Investigation of silicon on insulator fabricated by two-step O + implantation.Silicon-on-insulator wafers offer a number of advantages over bulk silicon wafers, such as high speed operation, low power consumption, anti-radiation, simple process and greater packaging densities. Now, it has been widely used in low-power/low-voltage and high-speed ultra-large-scale integrated (ULSI) circuits [1], micro-electro-mechanical system (MEMS) [2−4], high-voltage power devices [5] and optical waveguides [6]. Separation by implanted oxygen (SIMOX) is one of the leading techniques for synthesizing SOI wafers because it provides an excellent thickness uniformity of both the top Si and buried oxide (BOX) layers. Traditionally, the most widely used high dose SIMOX wafer is produced by implantation of more than 1.8×10 18 cm −2 16 O + at 550°C, which results in a BOX layer thickness of about 400 nm. However, the high dose implantation gives *Corresponding authors (rise not only to a high density of threading dislocations in the top Si layer, but also to a high production cost. In recent years, there has been a growing interest in low/medium-dose SIMOX (dose <1×10 18 cm −2 ) [7], with a BOX layer thickness of 50−200 nm, because of potential technological and economic advantages over high-dose SIMOX. These involve drastically reduced production cost and threading dislocations, improved device performance and thermal conductivity. For instance, it is reported that a thin BOX layer formed by low dose oxygen implantation is effective on reducing the self heating effect in metal-oxidesemiconductor field effect transistors [8]. However, as the implantation dose is reduced, the BOX layer tends to have discontinuities including breaks and high density of silicon islands. It is reported that Si islands are responsible for increased electrical leakage current through the BOX [9], or in extreme cases, its dielectric breakdown [10]. Many efforts