MICROELECTRONIC ENGINEERING ELSEVIER Microelectronic Engineering 28 (1995) 83-86 Study of RTS noise in degraded submicron polysilicon-emitter bipolar transistors D. Pogany and J.A. Chroboczek France Ttlecom CNET Grenoble, 28, chemin du Vieux Chene, B.P. 98, 38243 MEYLAN CEDEX, France The random telegraph signal (RTS) noise is studied in the time domain on submicron area CMOS-compatible bipolar junction transistors after hot carrier stressing. The degradation, recovery and noise properties of the devices are discussed in terms of defect states located at/near the Si/SiO2 interface under the oxide spacer. 1. INTRODUCTION High doping in downscaled CMOS-compatible bipolar transistors renders such devices susceptible to hot carrier degradation of the Si/SiO2 interface at the perimeter of the emitter-base (E-B) junction [ 1,2]. The degradation is observed as an increase in the base current and low- frequency noise. The latter usually exhibits an l/f character [3,4] and, as reported recently, random telegraph signal (RTS) noise can be observed in submicron area devices [5]. We present a more detailed analysis of RTS noise in degraded bipolar transistors and interpret the data in terms of properties of the defects created at/near the Si/SiO;! interface. The degradation and recovery phenomena are also discussed. 2. METHOD AND RESULTS Bipolar junction transistors, having the dimensions of 0.7 pm x (1.4 or 2 pm - spacer length), prepared using an advanced CMOS-compatible process developed at ihe CNET, have been studied [6]. The process involves, in particular, the formation of a 1OOA thermal oxide layer prior to the PECVD spacer oxide deposition. In order to establish the effect of hot carrier degradation, the base current and noise were measured before and after degradation in the 80- 3 15K temperature range. We studied the current fluctuations in the time domain by means of a rapid I-V converter and a digital oscilloscope. The principal advantage of this novel approach to the study of stress effects in advanced bipolar devices lies in its direct link with defect properties. The degradation of the E-B junction, performed at room temperature under different reverse biases (-7.5V<Unn <-5V) and durations (lo-60 min.), results in an increase in base current I, and noise. Typical I&J,,) curves before and after degradation are shown in Figure 1. We also monitored a temporal evolution of the base current during stress. Typically, at a fixed bias, the current is seen to increase slowly and then to fluctuate between two (or more) values (e.g. amplitude AI, = 1OpA at U,,=-5.7V). Abrupt current increments, as shown in the inset of Figure la, were also observed. Generally, the increase in I, is accompanied by an increase in the chaotic (I/f, noise background. At higher U an, the current and noise increase is much faster and discrete current fluctuations are higher (20-80pA at I,&=-5.9V; see inset of Fig. la). 0167.9317/95/$09.50 Q 1995 - Elsevier Science B.V. All rights reserved zyxwvutsrqponmlkjihgfedcbaZYXWVUTS SSDZ 0167.9317(95)00021-6