The influence of N2/H2 and ammonia N source materials on optical and structural properties of AlN films grown by plasma enhanced atomic layer deposition

Abstract

a b s t r a c tThe influence of N 2 /H 2 and ammonia as N source materials on the properties of AlN films grown by plasma enhanced atomic layer deposition using trimethylaluminum as metal source has been studied.The $-2Y grazing-incidence X-ray diffraction, high resolution transmission electron microscopy, and spectroscopic ellipsometry results on AlN films grown using either NH 3 or N 2 /H 2 plasma revealed polycrystalline and wurtzite AlN layers. The AlN growth rate per cycle was decreased from 0.84 to 0.54Å/cycle when the N source was changed from NH 3 to N 2 /H 2 . Growth rate of AlN remained constant within 100-200 1C for both N precursors, confirming the self-limiting growth mode in the ALD window. Al-Al bond was detected only near the surface in the AlN film grown with NH 3 plasma. AFM analysis showed that the RMS roughness values for AlN films grown on Si(100) substrates using NH 3 and N 2 /H 2 plasma sources were 1.33 nm and 1.18 nm, respectively. The refractive indices of both AlN films are similar except for a slight difference in the optical band edge and position of optical phonon modes. The optical band edges of the grown AlN films are observed at 5.83 and 5.92 eV for ammonia and N 2 /H 2 plasma, respectively. According to the FTIR data for both AlN films on sapphire substrates, the E 1 (TO) phonon mode position shifted from 671 cm À 1 to 675 cm À 1 when the plasma source was changed from NH 3 to N 2 /H 2 .

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films

“…11 More recently, plasmaenhanced atomic layer deposition (PEALD) has been demonstrated as an alternative method for AlN deposition. [12][13][14][15][16][17][18][19][20][21][22] The AlN process is also available for thermal ALD but in that case the source material selection is limited and above 400 C deposition temperatures are required. 15 In contrast, the attractive properties of PEALD films include low temperature processing (typically below 300 C), thus increasing the choice of precursors and materials, enabling tunable material properties, and still allowing the typical ALD thickness control below 1 nm accuracy.…”

“…Therefore, such conclusion made by Alevli et al based on their x-ray photoelectron spectroscopy and FTIR analysis about their PEALD AlN is questionable. 13 A broad FTIR valley ranging from 2280 to 2060 cm À1 and having the center around 2135 cm À1 is present in the samples from the as-deposited to the samples annealed at 800 C. This mode can be attributed to (NN) vibrations of the Al-N 2 complex. 28,49 The FTIR valleys exhibit a clear shift to higher wavenumbers and broadening as the annealing temperature increases.…”

“…Examining previous studies on PEALD AlN deposited at various temperatures reveals that typically the films are found to be crystalline. More specifically, usually PEALD films with a high Al:N ratio (>0.9) are found to be crystalline, [13][14][15][16][17][18][19][20][21] whereas AlN films with a low ratio (<0.9) are not found to be crystalline. 15,22 The additional nitrogen beyond the stoichiometric 1:1 ratio can be thought to be an impurity which affects the stability of the amorphous structure.…”

(Invited) Plasma-Enhanced Atomic Layer Deposition of III-Nitride Thin Films

“…Therefore we lowered the deposition temperatures by activating NH 3 or N 2 /H 2 through remote plasma and deposited polycrystalline wurtzite AlN thin films at temperatures ranging from 100-500 °C (10)(11)(12). Deposition parameters were optimized for these processes to achieve true ALD conditions.…”

Low‐temperature hollow cathode plasma‐assisted atomic layer deposition of crystalline III‐nitride thin films and nanostructures

“…Although thermal ALD (or atomic layer epitaxy, ALE) of III-nitride thin films, especially AlN, using various types of group-III precursors has been the focus of interest in the 1990s, current trend in the field of III-nitride ALD research is directed towards UV-, hot-wire-or plasmaassisted processes using metalorganic precursors [1][2][3][4][5][6][7][8][9][10][11]. Recently, we showed that ALD-grown III-nitride thin films may suffer from plasma-related oxygen contamination depending on the choice of N-containing plasma gas (N 2 , N 2 /H 2 or NH 3 ) [12,13].…”