Atomic layer deposition of AlN from AlCl3 using NH3 and Ar/NH3 plasma

Abstract

The atomic layer deposition (ALD) of AlN from AlCl 3 was investigated using a thermal process with NH 3 and a plasma-enhanced (PE)ALD process with Ar/NH 3 plasma. The growth was limited in the thermal process by the low reactivity of NH 3 , and impractically long pulses were required to reach saturation. Despite the plasma activation, the growth per cycle in the PEALD process was lower than that in the thermal process (0.4 Å vs 0.7 Å). However, the plasma process resulted in a lower concentration of impurities in the films compared to the thermal process. Both the thermal and plasma processes yielded crystalline films; however, the degree of crystallinity was higher in the plasma process. The films had a preferential orientation of the hexagonal AlN [002] direction normal to the silicon (100) wafer surface. With the plasma process, film stress control was possible and tensile, compressive, or zero stress films were obtained by simply adjusting the plasma time.

Comparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films

“…Interestingly, our results demonstrate stress level control achieved with the control of the bias voltage of the CCP reactor operated in remote mode during NH 3 plasma: bias voltage of ∼10 V induced a 220 MPa tensile stress while 25 V induced a −47 MPa compressive stress. Similarly, Rontu et al 8 have showed remote ICP based PEALD AlN film stress tuning to be possible from tensile to highly compressive by altering the plasma time of the AlCl 3 /NH 3 process. In addition, Goerke et al 34 showed minor ICP power dependency to film stress with the TMA/ N 2 :H 2 PEALD process at 150°C.…”

“…The presented GIXRD results are also supported by the density, roughness, and Al/N ratio results which were higher for films showing the lowest FWHM thus indicating a higher degree of crystallinity (especially the PA_25V and the PA_300C). In previous PEALD AlN studies, the degree of crystallinity has been shown to extend from amorphous 7,24 to polycrystalline 8,26 and even to the epitaxial grade [the (002) rocking curve being 144 arcsec] 44 depending on the process parameters, chosen substrate, surface treatment, and PEALD reactor setup. These aspects affect the impurity levels which in turn are known to affect crystallinity.…”

“…Therefore, AlN has been grown with several deposition methods, such as sputter deposition, 3 metalorganic chemical vapor deposition, 4 molecular beam epitaxy, 5 plasma enhanced chemical vapor deposition, 6 and plasma enhanced atomic layer deposition (PEALD). 7,8 Despite this, there is a lack of systematic comparison between the two main thin film deposition types: physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods of AlN. Specifically, the comparative mechanical performances of the films made with these methods have not attracted much academic attention.…”

“…20 However, the thermal ALD of nitrides suffers from poor reactivity of the conventional nitrogen precursors [e.g., ammonia (NH 3 )] at typical ALD temperatures (≤500°C) which has a negative effect on the film quality. 8,21 In order to overcome the issue of the low reactivity in thermal ALD, PEALD is commonly applied in which the nitrogen precursor is plasma activated. 22 PEALD of AlN has been studied reasonably during the last decade with studies mainly concentrated on the PEALD process parameters' influence on the growth behavior 8,23,24 and the chemical, 7,25 structural, 8,26 optical, 26 and electrical 27 quality of the AlN films.…”

“…8,21 In order to overcome the issue of the low reactivity in thermal ALD, PEALD is commonly applied in which the nitrogen precursor is plasma activated. 22 PEALD of AlN has been studied reasonably during the last decade with studies mainly concentrated on the PEALD process parameters' influence on the growth behavior 8,23,24 and the chemical, 7,25 structural, 8,26 optical, 26 and electrical 27 quality of the AlN films. However, important mechanical properties, such as adhesion, friction and wear, hardness, and elastic modulus, have not yet been studied despite their high importance for material reliability in mechanical applications and challenging environments.…”