Hot-Wire Generated Atomic Hydrogen and its Impact on Thermal ALD in TiCl₄/NH₃System

Abstract

We present the generation of atomic hydrogen made by the dissociation of molecular hydrogen upon collision with a tungsten (W) filament kept at a high temperature (T ≈ 1600-1900 • C). We demonstrate the ability to create atomic hydrogen and to introduce it in short pulses in experiments on etching of tellurium (Te) films. We further utilize the generated atomic hydrogen (H) to explore its impact on surface reactions in the TiCl 4 /NH 3 precursor system. Atomic hydrogen is introduced in pulses additionally to TiCl 4 and NH 3 with different pulse sequences. For the TiCl 4 /NH 3 /H sequence, there is no influence on the process compared to the ALD without H-pulses. The growth rate remains at 0.02 nm/cycle and the oxygen (residual gas) content -at 3-5 at%. For the TiCl 4 /H/NH 3 pulse sequence, the growth rate decreases to 0.01 nm/cycle and the oxygen content increases to 30-35 at%. Only TiCl 4 /H pulses result in no growth after the formation of approximately one monolayer. Similar effect occurs after introducing NH 3 via the hot filament, pointing to the decomposition of NH 3 and the formation of atomic hydrogen.It has been projected in the International Technology Roadmap for Semiconductors (ITRS) that new materials will be intensively introduced, starting from 2018, to replace or to be integrated with silicon in integrated circuits. 1 The coming era of new materials naturally implies a development of new technologies, new processes, and new precursors. Atomic Layer Deposition (ALD) is an excellent example of a process to realize new materials.ALD has a constantly growing market for deposition of dielectric, semiconductor and metallic layers of various functionalities where excellent optical, mechanical, electrical or chemical properties are required. The most important advantage of ALD over other deposition techniques is its capability to deposit films of uniform thickness on arbitrarily shaped and patterned surfaces, and controlling the thickness with a very high precision. Thermal ALD processes are commonly used to deposit compounds. Single-element films of metals and semiconductors, which become increasingly important for industry, are however very difficult to deposit using thermal-only ALD processes. 2 A solution in this case is plasma-enhanced ALD (PEALD), also called radical-enhanced ALD (REALD). Hydrogen-or nitrogen-based plasmas are used for PEALD of Ta(N), Ti(N), Ru, Si and Ge, 3-11 Al 12 as well as AlN 13 and GaN. 14 Pt can be grown using remote O 2 plasmas; 15 PEALD of Al 2 O 3 demonstrates better film properties compared to the thermal process. 16,17 In this work, we explore an alternative technique to generate radicals without plasma. We choose processes where dissociation of a certain precursor to form radicals can be achieved due to collisions with a hot tungsten (W) filament heated up to a temperature in the range of 1600-1900 • C. A plasma-based source of atomic hydrogen is substituted by the hot-wire source. This ensures that only molecular and atomic hydrogen are present in the gas phase, i.e....

Hot‐Wire Assisted ALD: A Study Powered by In Situ Spectroscopic Ellipsometry

“…Consequently, the newly developed surface will be more reactive to residual oxidants, resulting in its enhanced oxidation. Finally, the introduction of at‐H between TiCl 4 and NH 3 pulses leads to 35–40 at% of oxygen (instead of the original 3–4 at%), as measured by XPS . This confirms the previous considerations.…”

“…The appearance of the shoulder between 30 and 40 min of deposition (cf. Figure ) can be explained by the redeposition of tellurium from dissociation of H 2 Te . To note, in our earlier work the successful delivery of at‐H even over a longer distance of ≈70 cm (also with a 90° turn) was demonstrated …”

“…It is further reported that the by‐product of the etching reaction (H 2 Te) can be decomposed even at room temperature . To note, Te cannot be etched by molecular hydrogen . Real‐time monitoring of reduction of the Te film thickness, while introducing hydrogen gas via the hot‐wire setup, can therefore prove both the generation and the delivery of atomic hydrogen from the HW to the substrate.…”

“…On the contrary, the introduction of atomic hydrogen after each TiCl 4 pulse, i.e., after the surface is covered with chlorine (Cl), results in a much lower GPC . The Cl‐terminated metal site will be reduced by at‐H into releasing HCl, and is expected to contain Ti‐terminations.…”

Hot-wire assisted ALD of tungsten films:In-situstudy of the interplay between CVD, etching, and ALD modes

“…It appears from both experiments and simulations that a W film thinner than 30 nm is sufficiently transparent for SE measurements.The distance between the at-H outlet and the substrate was approximately 70 cm. To note, the efficient delivery of at-H from the hot-wire to substrate in the pressure range studied in this work was previously confirmed by separate experiments on etching of tellurium (Te) films by at-H [17]. The advantage of this design, despite a long diffusion distance required, was that the wafer could be protected from the damage caused by the hot-wire radiation.…”