Interdiffusions in thin-film Au on Pt on GaAs (100) studied with Auger spectroscopy

Abstract

It has been proposed that interdiffusion of Pt, Au, and GaAs constitutes one major source of instability in GaAs microwave devices with Pt/Au metallization. In order to determine the extent of interdiffusion of these materials, preparations of Pt/GaAs and Au/Pt/GaAs were heat treated over the range 250–500 °C, and chemical depth profiles were obtained by measuring the surface composition with Auger electron spectroscopy while ion milling. Platinum films were 125–9000 Å thick. When Pt/GaAs was heated in vacuum, the Pt-GaAs interaction initiated with a rapid migration of Ga into Pt and simultaneous formation of an As-rich layer at the Pt/GaAs interface. Gallium eventually traveled the entire thickness of even the 9000-Å Pt film while arsenic stopped abruptly at a distance ∼2/3 of the way into the Pt. Little or no Au was detected (<1 at.%) in the Pt or GaAs after extensive Pt/GaAs reaction in Au/Pt/GaAs. The reacted Pt film displayed a multilayered structure with each layer containing different amounts of Ga, As, and O. Pt/GaAs heated in air behaved similarly with two added features: a surface layer containing mostly Ga and O formed over the Pt, and oxygen diffused through the (reacted) Pt to form an oxygen-rich layer at the Pt/GaAs interface. Interdiffusion (during air anneal) was found to be reduced when the GaAs was oxidized prior to Pt deposition.

The new intermetallic compound Ga5Pt:Structure from a twinned crystal

“…The final data set used for the refinement of all the atomic positions and anisotropic displacement parameters (Table 4) contained 3005 unique reflections of which 2327 observed with I > 2s(I). The structure was solved in space group P2 1 /m and refined to agreement factors R1 (wR2) of 0.0484 (0.1137), the twin fraction converged to 0.637 (2). As expected, the atomic arrangement reminds the ordered part of the orthorhombic Cmcm cell but disorder has definitely vanished.…”

“…Actually this structure displays some covalent-like bonding interactions within the gallium sublattice and more particularly between gallium and platinum atoms. The overlap populations calculated by CASTEP are 0.55 for PteGa(1) (2.598 Å) and also for PteGa(2) (2.569 Å) while they are 0.26 (2.612 Å) and 0.37 (2.885 Å) for Ga(2)eGa (2). Although the PtePt distance (2.776 Å) is in the order of that in pure metal (2.77 Å, CN 12), the calculated overlap population is weak, 0.05 against 0.50 in the metal.…”

“…It has been reported that degradation of the interface rapidly occurs at elevated temperatures, due to solid state reactions between Pt and Ga [1,2]. Scanning electron and ion microscopy analyses of a 2000 Å platinum deposit on GaAs have revealed apparent imperfections in the Pt film surface after a 400 C annealing.…”

The thermodynamic assessment of the As–Pt system and the analysis of the Pt/GaAs interfacial reactions

“…And the interfacial reactions between the thin-film Pt and the substrate GaAs were studied by many investigators [3][4][5][6][7][8][9][10][11]. Different phase sequences, the apparent spatial sequences of the interfacial reaction products of those two joints, were obtained.…”

Thin film reactions on alloy semiconductor substrates

“…In the case of Pt/GaAs, the Ga diffuses out from the substrate at fairly low temperature [SI73,CC75], with the remaining As reacting with the Pt overlayer to form PtAs 2 .…”