The Effects of Surface Capping during Annealing on the Microstructure of Ultrathin SIMOX Materials

Abstract

The effects of a protective capping layer on the microstructure of ultrathin separation by implantation of oxygen ͑SIMOX͒ materials formed by ion implantation were studied using transmission electron microscopy. A set of SIMOX wafers were implanted at 65 keV in a dose range of 1.5 to 7.0 ϫ 10 17 O ϩ /cm 2 followed by a high temperature ͑1350°C͒ annealing with and without a protective cap. The lowest dose to form a continuous buried oxide ͑BOX͒ layer without Si islands at 65 keV is 2.0 ϫ 10 17 O ϩ /cm 2 without a protective cap and 2.5 ϫ 10 17 O ϩ /cm 2 with a protective cap. Above 2.5 ϫ 10 17 O ϩ /cm 2 under both annealing conditions, the BOX layer formed continuously but with Si islands present. The uncapped samples show slightly lower density of Si islands. Oxygen from the annealing ambient can diffuse in the uncapped samples through the thin top Si layer, which helps the BOX layer grow laterally and lower the Si island density. The density of defects in the top Si layer is also slightly lower in the uncapped samples because of the ability of Si interstitials to incorporate into the surface and the effective annihilation of extended defects during the final annealing step. The top Si layers of the uncapped samples are thinner than those of the capped samples due to surface thermal oxidation.The development of high quality ultrathin silicon-on-insulator ͑SOI͒ substrates is essential for the emerging submicrometer technology and fully depleted applications. SOI substrates have many advantages over bulk Si substrates for isolation, process simplicity, for short channel device performance, and for applications involving low power, high speed, high temperature, and radiation hardness. [1][2][3][4][5] Of the several SOI technologies, the most advanced is the synthesis of a buried oxide ͑BOX͒ layer by the separation by implanted oxygen ͑SIMOX͒ technique. 6 Conventionally, SIMOX wafers are produced by implanting high dose high energy oxygen ions ͑1.8 ϫ 10 18 O ϩ /cm 2 , 200 keV͒ into Si wafers. This process is expensive because it requires a long implantation time. In addition, the wafers produced by this technology contain a relatively high density of threading dislocations in the top Si layers. In order to overcome these problems, the low dose SIMOX technique was introduced. However, the low dose BOX layer is inferior to that of the high dose SIMOX in terms of electrical characteristics and reliability. Recently, it has been shown that the integrity of thin BOXs can be improved by annealing in a highly oxidizing ambient. 7 The same method has also been used to successfully produce thin film SIMOX wafers through surface oxidation. 8,9 However, a high production cost is incurred from the additional processing steps.A direct and cost-effective way to reduce the thickness of the top Si layer and the BOX layer is to decrease both the implantation energy and the oxygen dose. Reducing the implantation energy decreases the spread of the implanted ions which makes it possible to form a continuous BOX layer at lower doses whic...

Microstructural evolution of low-dose separation by implanted oxygen materials implanted at 65 and 100 keV

“…The SOI film must be as thin as is feasible, and the uniformity of the Si film thickness is a prime prerequisite for minimizing the materials used and the processing cost, as well as to have the resulting devices be capable of operating at low power and at low voltage. Recently, Anc et al 12 and our group 13,14 investigated the effects of the implantation dose (from 1.5 to 7.0 × 10 17 O + /cm 2 ) and annealing conditions (with and without surface capping) for 65 keV with a higher beam current (≈40 mA), a much higher value than previously reported. The original SIMOX process for the manufacture of SOI wafers was developed over 20 years ago.…”

“…The original SIMOX process for the manufacture of SOI wafers was developed over 20 years ago. 14 In this research, further efforts were made to understand the correlations between process parameters (energy, dose, and annealing temperature) and the formation of the BOX layer and defects during the annealing process in the low-dose, low-energy SIMOX. A great deal of effort was aimed at improving the quality of the Si overlayer by using a higher beam current, a higher implantation temperature, and sequential implantation and annealing techniques.…”

A numerical model to simulate precipitate growth and ripening in oxygen-implanted silicon-on-insulator materials

“…The smaller dimensions-one-tenth that of conventional SIMOX, however, require superior quality of the Si top layer, the BOX layer and interfaces. Therefore, the study of defect and precipitate formation and evolution during the SIMOX process is important for the development of ultrathin SIMOX (Johnson et al 2001).…”

Fixed mesh front‐tracking methodology for finite element simulations

“…This has been chosen to illustrate the capabilities of the method to model problems involving larger numbers of interfaces that undergo complex splitting and merging. The process models the time evolution during annealing of the silica precipitates from an as-implanted distribution to form a buried oxide insulator layer in a process known as SIMOX [23,24]. The process requires the simulation of the interactions of large numbers of precipitates which can grow, dissolve, merge or split and provides an ideal testing ground for front tracking techniques.…”