Implant isolation of InP and InGaAs by proton irradiation at variable doses and substrate temperatures

Abstract

The evolution of the sheet resistance (Rs) of n-type InP and InGaAs layers bombarded by protons with doses in the range of 1~1 0 '~ -4~1 0 '~ cm-2 at substrate temperatures RT and 2OO0C was investigated. The n-type doped layers for both InP and InGaAs of thickness lpm were grown on semi-insulating (SI) InP substrate of <loo> orientation using molecular beam epitaxy (MBE). A uniform damage density was formed within the conductive layer by proton implantation at 250 keV to isolate the structure. Resistivity and Hall effect measurements were performed in order to study the evolution of the sheet resistance as a function of dose. An optimum isolation of 1x106 and 2x104 ohmshquare was obtained at a threshold dose of 4~1 0 '~ and 4~1 0 '~ cm-2 for InP and InGaAs layers implanted at RT, respectively. For 2OO0C implants, a lower isolation value of -5x103 ohmshquare was obtained at a threshold dose of 4 x1013 and 4~1 0 '~ cm-2 for both InP and InGaAs layers, respectively. This data suggests that, for the isolation scheme used most of the defects are already annealed out near 200°C, which explains the behaviour of the sheet resistance in the case of 2OO0C implants. The antisite defects formed by the replacement collisions are thought to be responsible for the isolation formed in InP and InGaAs by virtue of their lower sensitivity to dynamic annealing. These results can be used to choose the right implant conditions in order to provide effective electrical isolation of In-based devices. IntroductionIon implantation is an essential process step in the production of integrated circuits (ICs) in both silicon and compound semiconductor technologies. In the case of 111-V compound semiconductors, there are two important applications. The first is the creation of n-or p-type doped layers by implantation of dopants followed by an annealing process [l]. The second is the implantation of ion species like hydrogen, helium, boron, oxygen, nitrogen, iron, argon, etc. to convert a doped layer into a highly resistive one [2]. This latter application is called implantation induced isolation or isolation by ion irradiation. Device/device parasitic effects are a serious issue in integrated circuits and these are minimized by rendering conductive material between devices semi-insulating through ion implantation [3] or alternatively, removing the conductive material through mesa etching. Implant isolation is advantageous as the surface planarity is maintained, higher throughput is obtained compared to mesa etch and, in general, less intrusion under the mask edges is observed [4].