Hafnium-related photoluminescence in single crystal silicon

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Hafnium-related photoluminescence in single crystal silicon R. Sachdeva1,2, A. A. Istratov1,2, Wei Shan2, P. N. K. Deenapanray3, and E.R. Weber1,2 1

Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 Lawrence Berkeley National Laboratory, MS 62-203, 1 Cyclotron Rd., Berkeley, CA 94720 3 Center for Sustainable Energy Systems, The Australian National University, Canberra, Australia 0200 2

ABSTRACT A new photoluminescence (PL) band in the energy range of 700 meV to 950 meV associated with hafnium implanted in silicon is reported. A shift in the position of photoluminescence peaks observed on the samples implanted with two different isotopes of Hf confirms the Hfrelated origin of the observed photoluminescence band. Activation of the Hf-optical centers requires a 1000°C anneal step. The intensity of the PL lines depends on the cooling conditions. The spectrum consists of five peaks in the rapidly quenched sample as opposed to twenty one in the slowly cooled sample. Temperature dependent PL measurements and hydrostatic pressure measurements were performed to identify their nature.

INTRODUCTION There has been much interest in replacing silicon dioxide in CMOS transistors and using gate dielectric films with high dielectric constants. Among the high-k dielectrics - ZrO2, HfO2, Ta2O5, and Al2O3, etc., have high dielectric constants but the most promising in terms of meeting the requirements and improving the performance of Si devices appears to be HfO2 [1, 2]. Introduction of HfO2 in silicon device production makes possible unintentional contamination of underlying silicon with Hf. Therefore, it becomes important to understand the electrical and optical properties of Hf in Si. Electrical levels of Hf in Si observed in samples doped with Hf during crystal growth were reported by Lemke [3]. However, there is hardly any data on optical properties of Hf in Si. In our investigation, we report observation of a PL signal of Hf in Si in the energy range of 700 meV to 950 meV and describe the general features of the emission spectra, its dependence on temperature, excitation and hydrostatic pressure.

EXPERIMENTAL PROCEDURES

N-type Czochralski (CZ) silicon wafers with a resistivity of 5 – 10 Ω-cm were implanted with hafnium at an energy of 50 keV and dose of 1013 cm-2. Some p-type CZ samples were also implanted and showed similar results as n-type silicon. The isotope 180 Hf has been implanted in the silicon samples, with the exception of the isotope substitution experiments where samples implanted with 178 Hf and 180 Hf were compared. Samples were annealed in a horizontal furnace in Ar ambient in three steps: 650°C for 30 min, then 1000°C for 3 hrs, and then cooled to room temperature. The first step is often used to anneal out implantation induced damage and restore crystallinity [4]. The second step (1000°C) is needed to activate Hf. Two different cooling rates were used to cool the sample from the annealing temperature of 1000°C to room temperature. The first one, slow furna