Interface Characteristics of SiO[sub 2]/Si Structure with High Energy Boron Implantation

Abstract

Boron profiles and interface characteristics of SiO 2 /Si structure when boron was implanted by high energy implantation were studied. A very narrow ͑ϳ0.3 m͒ channel-stop layer can be formed under a 1.5 m thick SiO 2 layer by high energy B ϩ implantation. An ion dose of 1.5 ϫ 10 12 ions/cm 2 is adequate to form a channel-stop layer. The surface state density was 2.2 ϫ 10 11 /cm 2 after implantation and decreased to a value of 1 ϫ 10 11 /cm 2 following 1 h of heat-treatment at 1000°C. The surface state density was decreased by heat-treatment and recovered to a value equal to that of nonimplanted samples.High energy ion implantation into silicon is used in ultralargescale integration ͑ULSI͒ fabrication processes because it can be used to control electrical properties in layers within a few micrometers from the surface. 1-5 It can provide a technique to form a buried layer, a retrograde well, and proximity gettering. 2 Particularly, latch-up susceptibility of complementary metal oxide semiconductor ͑CMOS͒ circuits can be improved. 6 The use of N ϩ grids or p ϩ buried layers to reduce alpha-particle-induced soft errors in memory devices has also been proposed. 7 Device isolation was improved by high energy implantation through a field oxide. 1 Recently, multiple high energy ion implantations were used to generate profiled wells. 3 By employing multiple, high energy ion implantations, a profiled well can easily be implemented in a high performance CMOS. Otherwise, high energy ion implantation causes severe damage to the crystalline lattice. 8-10 One reason for using relatively low concentration buried layers in device applications is to avoid the adverse effects of implanted damage.In the case of a typical local oxidation of silicon ͑LOCOS͒ process, boron implantation with low energy is performed before field oxide formation. Then, boron is diffused during oxidation, that is, diffused to several micrometers from the bottom of the oxide film. Particularly, the carrier concentration decreases at the SiO 2 /Si interface due to segregation. The boron diffusion depth becomes large due to the high temperature and long time heat-treatment used to form the field oxide.Device isolation is improved by high energy implantation through a field oxide. For its realization, high energy ion implantation can be successfully applied to fabricate a channel-stop P ϩ layer after fabricating a LOCOS isolation structure. Little is known about impurity profiles and electrical activation characteristics for device fabrication processes. This paper reports on boron profiles and interface characteristics of a SiO 2 /Si structure when boron was implanted with a high energy implantation system of a 2.5 MeV Van de Graaff accelerator. ExperimentalThe substrate used in this experiment was a ͑111͒ oriented, p-type silicon wafer with a resistivity of 8-12 ⍀ cm. After standard initial cleaning, silicon oxide layers with a thickness of 0.15 or 1.5 m were formed on the wafers by pyrogenic oxidation at 1150°C.The wafers were implanted with boron ions at e...