Deposition temperature dependence of electrical instability in an InP metal-insulator-semiconductor capacitor provided by plasma-enhanced chemical vapour deposited silicon nitride

Abstract

InP is an important material for high-speed devices and is well suited for metal insula tor-semiconductor (MIS) technologies due to the large drift velocity of electrons and the lower density of surface states at an insula tor-InP interface than at an insulatorGaAs interface. Although many successful devices have been built and demonstrated, the devices still suffer from electrical instabilities such as drain current drift and/or flatband voltage shift [1, 2]. These electrical instabilities have been attributed to insulator traps [3-5], surface states [6] and bulk traps in InP [7]. In this letter we report the flatband voltage shift after bias-stress in an InP MIS provided by plasma-enhanced chemical vapour deposition (PECVD) of silicon nitride. We varied the deposition temperature from 240 to 330 °C and the results are explained by a model in which electrons tunnel from the substrate into insulator traps [5]. The MIS capacitors used in this study were fabricated on (100) undoped InP wafers with a carrier concentration of 5 x 10 ~s cm -3. The wafers were cleaned in standard organic solutions (trichloroethylene, acetone and methanol) and then rinsed in deionized water. To remove the native oxide on the surface, the wafers were then etched in sequence with acid solution (H2SO4:H202:H20 = 3:1:1) for 60s and HF (49%) solution (HF : H 2 0 = 1 : 1) for a further 60 s. After rinsing in deionized water, the wafers were blow-dried with nitrogen. Silicon nitride films were deposited using PECVD apparatus designed in-house [8], of which the reactor was a hot-wall capacitively coupled type, from dilute silane (5% SiH4 in N2), ammonia (99.999% purity) and nitrogen (99.9999%) gas mixtures with a gas pressure ratio of SiH4:NH3:N2 = 3:1:5, a total pressure of 120 Pa and an r.f. power of 30 W. For oxygen-free silicon nitride film the reactor was heated at 300 °C and purged with dry N2 gas flow for 1 h before silicon nitride deposition. First we deposited a capping silicon nitride layer by PECVD at a deposition temperature of 300 °C before backcontact formation. The back contact was then formed by evaporation of Ni /AuGe/Ni /Au and heat treatment at 480 °C for 90 s in an H2 atmosphere. After the back-contact was formed the capping layer was removed in buffered HF solution and the wafer