Plasma enhanced atomic layer deposition of aluminum sulfide thin films

Abstract

Aluminum sulfide is a promising material for energy storage, photonics, and microelectronics applications. Most of these applications require thin films with a high control over layer thickness and composition making atomic layer deposition an ideal deposition technique. The authors report a plasma enhanced process for aluminum sulfide based on trimethylaluminum and H2S-plasma. The growth characteristics were studied using in situ spectroscopic ellipsometry, indicating linear growth at a rate of 1.2 Å/cycle at 90 °C. Self-saturated growth could be achieved in a temperature window ranging from 90 to 350 °C. The process relies on combustion reactions during the plasma step, as confirmed by the observation of CS2 using in situ mass spectrometry measurements. Ex situ x-ray photoelectron spectroscopy, x-ray diffraction, and scanning electron microscopy/energy-dispersive x-ray spectroscopy measurements showed that the deposited layers are amorphous and pinhole free.

Atomic Layer Deposition of Al-Doped MoS2: Synthesizing a p-type 2D Semiconductor with Tunable Carrier Density

“…The position of the Al 2p peak suggests that Al is bonded to S. Another possibility that can be ruled out is the formation of Al 2 S 3 clusters. Although Al 2 S 3 exists and can be synthesized by ALD, 53 , 68 , 69 this material is a wide band gap insulator. 53 , 70 Therefore, formation of Al 2 S 3 inclusions on a large scale would almost certainly lead to an increase in resistivity with increasing Al concentration rather than the decrease observed in this work.…”

Plasma enhanced atomic layer deposition of gallium sulfide thin films

“…21 Recently, the use of H 2 S plasma instead of H 2 S opened the possibility for new ALD processes. [24][25][26] Especially, our previous results on plasma enhanced ALD (PE-ALD) of Al 2 S 3 are very promising for GaS x ALD. 26 The observation that thermal ALD of trimethylaluminum (TMA) þ H 2 S did not result in any growth while an ALD process could be established in combination with H 2 S plasma motivated us to try a similar approach for GaS x combining TMG with H 2 S plasma.…”

“…GaS x thin films were deposited in a home-built pump-type ALD reactor which was redesigned to be compatible with hydrogen sulfide following the suggestions described by Dasgupta et al 27 A detailed description of the used ALD system can be found in our previous work. 25,26 GaS x thin films were deposited by using TMG (.99%, Strem) as precursor. As a reactant pure H 2 S gas (for thermal ALD experiments) or H 2 S plasma diluted by Ar (1:3) (for PE-ALD experiments) was used.…”

“…In previous studies, we investigated the optical emission spectrum of H 2 S plasma. 25,26 These studies revealed the presence of H þ and S þ ions. Furthermore, H 2 S þ radicals were detected while no optical emission from the metals involved in the ALD process was found.…”

“…In analogy to the reaction mechanism of the thermal TMA þ H 2 O and plasma enhanced TMA þ O 2 plasma processes or the PE-ALD of Al 2 S 3 , a second reaction mechanism using H 2 S plasma can be proposed. [32][33][34]26 In this PE-ALD reaction [ Fig. 5(b)], the first half cycle is similar to the thermal ALD reaction: TMG reacts with free SH surface groups in order to form GaCH 3 surface groups and CH 4 .…”