Anuranjan Srivastava

ALD of Hafnium Oxide Thin Films from Tetrakis(ethylmethylamino)hafnium and Ozone

Hafnium oxide (HfO 2 ) thin films were deposited from tetrakis(ethylmethylamino)hafnium (TEMAH) and ozone (O 3 ) by atomic layer deposition (ALD) on 200 mm silicon wafers. The O 3 half-reaction shows good saturation behavior. However, gradual surface saturation is observed for the TEMAH half-reaction. Within wafer non-uniformity of less than 1% and step coverage of about 100% were achieved for trenches with aspect ratio of around 40:1. The film thickness increased linearly as the number of cycles increased. From susceptor temperatures of 160-420°C, the lowest deposition rate (A/cycle) and the highest refractive index is observed at 320°C. The atomic ratio of hafnium to oxygen determined by Rutherford backscattering is 1:2.04 for the films deposited at 320°C. The carbon and hydrogen content determined by secondary ion mass spectroscopy (SIMS) decreased as the susceptor temperature increased from 200 to 320°C. Lower carbon and hydrogen levels were obtained in the control films made with H 2 O than the films made with O 3 . A reaction mechanism of the TEMAH + O 3 ALD process is discussed. The results show that an O 3 -based ALD HfO 2 deposition is promising for microelectronic applications.

Engineered tantalum aluminate and hafnium aluminate ALD films for ultrathin dielectric films with improved electrical and thermal properties

Continued scaling of device dimensions requires deposition of high-quality thin films with a thickness of 50 angstroms or less. Nucleation effects in typical CVD processes make it difficult to achieve continuous films in this thickness regime. Atomic layer deposition (ALD), a technique developed over 25 years ago but applied to IC processing only recently, enables deposition of ultra-thin films with atomic-scale precision. This technique offers 100 percent step coverage of high aspect ratio features, as-deposited films which are amorphous and free of pinholes, excellent within-wafer uniformity and wafer-to-wafer uniformity, and favorable electrical properties. Moreover, ALD offers the opportunity to engineer material properties by creating layered structures (nanolaminates) and mixtures (alloys) which combine advantageous properties of different materials. These last features may be critical in efforts to replace silicon dioxide as the industrys dielectric workhorse if no single material emerges as a suitable direct replacement. The nanolaminate capability of ALD will be discussed with physical and electrical data on nanolaminates of aluminum oxide with tantalum pentoxide and aluminum oxide with hafnium oxide. Individual nanolaminate layers can be varied from tens of angstroms to as little as 1-2 atomic layers. Data for Al 2 O 3 /Ta 2 O 5 and Al 2 O 3 /HfO 2 alloys will also be presented demonstrating the ability to create materials with controlled, variable composition. The alloy and nanolaminate capabilities enable the creation of graded interfaces and atomically smooth transitions between different materials. Prospects for application of these materials to gate stacks and capacitors will be assessed.

Enhanced electrical properties of Ba0.5Sr0.5TiO3 thin films grown by ultraviolet-assisted pulsed-laser deposition

In this letter, we report enhanced electrical performance of high-dielectric-constant barium strontium titanate (BST) thin films grown by an in situ ultraviolet (UV)-assisted pulsed-laser deposition (UVPLD) technique. In comparison with conventional pulsed-laser deposition (PLD) BST (i.e., films grown under similar conditions but without UV illumination) and films grown by other techniques, the UVPLD-grown films exhibited improved structural and electrical properties. The dielectric constant of 40-nm-thick films deposited at 650 °C by PLD and UVPLD were determined to be 172 and 281, respectively. The density of interface states at the flat-band voltage was found to be approximately 5.6×1011 eV−1 cm−2 for the UVPLD-grown BST films, which was almost an order of magnitude lower than that obtained for conventional PLD films. The leakage current density of the UVPLD-grown films was approximately 4×10−8 A/cm2 at 100 kV/cm, which was nearly 1.5 times lower than that obtained from the PLD deposited films. The equ...