Atomic Layer Deposition of Aluminum Phosphate Based on the Plasma Polymerization of Trimethyl Phosphate

Abstract

Aluminium phosphate thin films were deposited by plasma-assisted atomic layer deposition (ALD) using a sequence of trimethyl phosphate (TMP, Me 3 PO 4 ) plasma, O 2 plasma and trimethylaluminium (TMA, Me 3 Al) exposures. In-situ characterization was performed, including spectroscopic ellipsometry, optical emission spectroscopy, mass spectrometry and FTIR. In the investigated temperature region between 50 • C and 320 • C, nucleation delays were absent and linear growth was observed, with the growth per cycle (GPC) being strongly dependent on temperature. The plasma polymerization of TMP was found to play an important role in this process, resulting in CVD-like behavior at low temperatures and ALD-like behavior at high temperatures. Films grown at 320 • C had a GPC of 3.7Å/cycle and consisted of amorphous * To whom correspondence should be addressed † Ghent University ‡ IMEC ¶ These authors contributed equally to this work 1 aluminium pyrophosphate (Al 4 P 6 O 21 ). They could be crystallized to triclinic AlPO 4 tridymite by annealing to 900 • C, as evidenced by high temperature XRD measurements. The use of a TMP plasma might open up the possibility of depositing many other metal phosphates by combining it with appropriate organometallic precursors.

Plasma-enhanced atomic layer deposition of vanadium phosphate as a lithium-ion battery electrode material

“…As mentioned in the Introduction, when using TMP plasma, a sufficiently high substrate temperature is required in order to inhibit the spontaneous plasma polymerization of TMP, which would result in PE-CVD instead of PE-ALD. Our previous studies using TMP plasma have established this temperature to be 300 C. 12,13,17,18 At this temperature, however, some metalorganic precursors will thermally decompose; this is also the case for our vanadium precursor candidates. From literature, the decomposition temperatures of VTIP and TEMAV are 200 and 175 C, respectively, so one would expect strong thermal decomposition of both precursors at 300 C. [23][24][25] To test their decomposition behavior, we ran experiments where we pulsed the precursors into the chamber onto a silicon substrate heated to 300 C, while using in situ ellipsometry to monitor film growth.…”

“…1 This comes at the expense of very slow growth (typically in the order of 1 Å /cycle), making ALD most suitable for very thin films. Although many different ALD processes have been developed for various classes of materials such as oxides, ii-vi and iii-v semiconductors, metal nitrides, metals, metal sulfides, and fluorides, 2 the existing reports on ALD of phosphates are still limited, [3][4][5][6][7][8][9][10][11][12][13] but have recently been increasing in number because of their relevance as electrode [14][15][16][17][18] or electrolyte [19][20][21][22] films in lithium-ion batteries.…”

“…[32][33][34] In this study, we present a plasma-enhanced atomic layer deposition (PE-ALD) process for vanadium phosphate. We incorporate phosphorus by means of a trimethyl phosphate (TMP) plasma; we have previously used this method successfully for PE-ALD of aluminum phosphate, 12 zinc phosphate, 13 iron phosphate, 17 and titanium phosphate. 18 Our plasma-enhanced method has the advantage of forming highly reactive phosphate species on the surface which easily react with a metalorganic precursor, typically resulting in high growth rates.…”

“…The drawback is that the substrate temperature must be sufficiently high in order to inhibit any spontaneous polymerization of the TMP plasma, which results in an undesirable CVD contribution. 12 This makes it more challenging to find a suitable metalorganic precursor; an insufficiently high decomposition temperature will result in thermal precursor decomposition and also yield an undesirable CVD contribution.…”

Bifunctional earth-abundant phosphate/phosphide catalysts prepared via atomic layer deposition for electrocatalytic water splitting

“…[21][22][23] Some of the authors have developed a plasma-enhanced (PE-ALD) method which has the advantage of having much higher growth per cycle (GPC) values than other processes, speeding up deposition times for thicker lms. 22,24 In this work, ALD was used to deposit cobalt and iron phosphate lms with electrocatalytic activity for both HER and OER. In addition, post-deposition thermal reduction was used to obtain phosphide electrocatalysts for HER.…”