DOPING OF OXIDIZED FLOAT ZONE SILICON BY THERMAL DONORS - A LOW THERMAL BUDGET DOPING METHOD FOR DEVICE APPLICATIONS ? R. JOB 1 , A.G. ULYASHIN 1 , Y.L. HUANG 1 , W.R. FAHRNER 1 , E. SIMOEN 2 , C. CLAEYS 2, 3 , F.-J. NIEDERNOSTHEIDE 4 , H.-J. SCHULZE 4 , G. TONELLI 5 1 University of Hagen, P.O. Box 940, D-58084 Hagen, Germany 2 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium 3 Electr. Eng. Dept., KU Leuven, Kasteelpark Arenberg 10, B-3001 Leuven, Belgium 4 Infineon AG, P.O. Box 80 09 49, D-81609 Munich, Germany 5 IFN, Via Livornese 1291, I-56010 Pisa, Italy ABSTRACT Thermal donor formation was studied in oxygen enriched high resistive float zone silicon (FZ Si:O i ). Such substrates are used e.g. for radiation hard detectors or high voltage devices. RF Plasma hydrogenation (110 MHz, 50 W) was carried out at 250°C for 1 hour. Subsequent annealing was done at 450°C/air for up to 50 h. The plasma treated and annealed FZ Si:O i samples were analyzed by spreading resistance probe, capacitance-voltage and DLTS measurements. It is shown that a rapid formation of donors can be observed in oxidized FZ Si:O i , but in a somewhat different way than in Czochralski (Cz) Si. While in Cz Si the hydrogen enhanced formation of 'old' thermal double donors occurs under the applied processes, in FZ Si:O i most probably the formation of new hydrogen related shallow donors can be assumed. 1. INTRODUCTION Hydrogen enhanced formation of oxygen related 'old' thermal double donors (TDDs) can be observed in Cz Si after applying a plasma hydrogenation at 250°C (60 min) and a subsequent annealing in air at 450°C (≥ 20 min) [1-4]. TDD concentrations up to ∼ 10 16 cm -3 were observed. Therefore, in p-type Cz Si a counter doping by TDDs and the formation of deep p-n junctions occur if the acceptor concentration is below 10 16 cm -3 . In n-type material deep regions with a graded doping can be created by the TDDs [5]. The controlled TDD formation can be used for a low thermal budget fabrication of devices with deep p-n junctions and/or graded doping profiles (e.g. high voltage or radiation detectors) [6, 7]. Normally highly resistive FZ substrates are used for such applications. By oxygen enrichment FZ Si can be made radiation hard [8-10]. But to obtain acceptable radiation hardness properties, the oxygen has to be located mainly at interstitial lattice sites. In Cz Si interstitial O i is a major constituent of TDDs. Therefore, hydrogen enhanced TDD formation might play a role also in FZ Si:O i , as we have recently speculated in [11]. On the other hand, hydrogen could be involved in the formation of other thermal donors species, i.e. the shallow thermal donors (STDs) [12-20], which are single donors. Oxygen most probably is also a constituent of these complexes. We will show that under the applied hydrogenation/annealing treatments in FZ Si:O i the formation of new hydrogen related shallow donors occurs and not a hydrogen enhanced TDD formation, as was observed in Cz Si. 2. EXPERIMENTAL The investigations were done on two kinds of oxidized n-type FZ silicon substrates with high resistivity, i.e. nominal 5 k Ωcm and 500 Ωcm wafers. In case of the 5 k Ωcm FZ Si, oxygen was incorporated into the material by the following procedure: i) oxygen enrichment of the wafer surfaces by 15 h dry Mat. Res. Soc. Symp. Proc. Vol. 719 © 2002 Materials Research Society F9.5.1