Structural characterization of damage in Si(100) produced by MeV Si + ion implantation and annealing
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I. INTRODUCTION
MeV ion implantation has not realized its anticipated potential in fabrication of integrated circuits in Si due in part to the lack of high-energy implanters with sufficient through-put capability and reliability suitable for production environments. While this situation is currently being remedied by commercial vendors of implantation equipment, there still remain manufacturing issues concerning process integration. Some of the process integration issues are very fundamental in nature, such as the effects of residual, ion-induced damage on device performance. In many of the MeV ion applications, ion-induced damage can have a deleterious effect on the desired result and must therefore be removed by post-implantation annealing. This is the case when high-energy ions are used to form a buried conductive layer to reduce the latch-up susceptibility of adjacent complementary devices in a CMOS integrated circuit.1 There are, however, novel applications which make use of the damage produced by the energetic ions: for example, the use of high-energy implantation through device structures to reduce the minority carrier lifetime in the active regions,2 or the formation of a buried damaged layer far from the active regions for impurity gettering.3 Clearly, there is a need for a full characterization of the nature of the damage produced by high-energy ions for different ion types and doses as well as the associated annealing behavior. Since many of the above applications involve high ion fluences (>1016 cm"2), the dam352
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age morphology produced by such doses is of particular interest. In this paper, a detailed characterization of the damage produced by 1.25-MeV self-ions and its annealing behavior in (100) Si single crystal is presented. The study was limited to self-ion implantation with 28Si+ ions to remove the possibility of chemical effects on the ion-induced damage/annealing process. Implantations were done at both room temperature (RT) and liquid nitrogen temperature (LN2). Generally, sufficiently high doses of ions were implanted at both temperatures to form a buried amorphous layer near the ions' end-ofrange (EOR). Morphological differences between the damage formed at the two temperatures are discussed. The annealing behavior of the ion-induced damage (in particular the buried amorphous layers) was determined at several different temperatures, accompanied by characterization of the nature of the residual damage. The results of the characterization revealed the formation of an extended two-phase region ahead of the buried amorphous layer at LN2 temperature which had an anomalously low recrystallization temperature. This is contrasted with the markedly different morphology of the amorphous layer formed at RT. A model is proposed to account for the observations. Also, mechanisms for the different growth velocities which were observed at the front and back interfaces of the amorphous layers are discussed. Both Rutherford backscattering spectroscopy (RBS) and cross-sectional
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