Analysis of Real-Time Hydrogenation data from P and N-Type Silicon
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ANALYSIS OF REAL-TIME HYDROGENATION DATA FROM P AND N-TYPE SILICON CARLETON H. SEAGER AND ROBERT A. ANDERSON Sandia National Laboratories, Albuquerque, NM 87185 ABSTRACT Hydrogenation of metal/thin oxide/p-type silicon and metal/n-type silicon diodes has been studied using high frequency capacitance profiling. In situ observations of acceptor and donor passivation were made while H ions were implanted through thin gate metallizations. Direct measurement of ion transits at a variety of electric fields establish that a unique mobility can be assigned to positive H ions, and modeling of low and high field data in both n and p-type samples is consistent with the notion that the positive charge state is occupied -1/10 of the time. The time dependence of hydrogen penetration for both p and n-type diodes indicates that hydrogen is, in addition to being trapped at unpassivated shallow donors or acceptors, becoming immobilized at other sites in silicon. The density of these secondary trapping sites correlates well with the shallow dopant population suggesting that additional hydrogen atoms may become trapped near already-passivated dopant atoms. INTRODUCTION The motion and trapping of hydrogen in silicon can be studied on a "real time" basis by implanting low energy protons through the thin metal gates of Schottky or thin oxide MIS structures while monitoring changes in the depletion layer charge density with capacitance techniques [1,2]. In a companion paper [3] presented at this symposium, we discuss the modelling of this implantation process and conclude that it results in the rapid establishment of a nearly time independent H density near the end of range in the semiconductor. This end of range depth is 50-250 A for the ion energies used in the present studies. In this work, we shall primarily concern ourselves with two additional features of the problem. The first is a direct estimate of ion mobilities obtained by measuring arrival times of H+ crossing trap depleted regions. The second is a full exposition of the field and time dependence of hydrogenation profiles in numerous p and n-type samples at various shallow doping
concentrations.
Sample preparation and measurement techniques have been discussed elsewhere in full detail [1,2]. All plots of charge density versus depth were obtained by 1 MHZ capacitance profiling of Schottky and MIS depletion regions during H introduction. Most of the samples discussed here were fabricated on or CZ silicon and had 400 A thick evaporated Al gates; however, a few were made from Edge Fed Growth (EFG), ribbon silicon, which has high concentrations of dissolved carbon and low interstitial oxygen content, and several others were fabricated from FZ silicon, which has 50-100 times less 0 than typical CZ material. Data obtained from these capacitors will be useful in assessing the importance of C or 0 in trapping H. ION TRANSIT EXPERIMENTS If hydrogen is introduced into a sample at time t=o and drifts into the bulk in the presence of an electric field E, the ion flux is given by: eDEH (1
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