High power pulsed magnetron sputtering (HPPMS) is an emerging technology that has gained substantial interest among academics and industrials alike. HPPMS, also known as HIPIMS (high power impulse ...

High power pulsed magnetron sputtering: A review on scientific and engineering state of the art

Atomic layer deposition (ALD) has been studied for several decades now, but the interest in ALD of metal and nitride thin films has increased only recently, driven by the need for highly conformal nanoscale thin films in modern semiconductor device manufacturing technology. ALD is a very promising deposition technique with the ability to produce thin films with excellent conformality and compositional control with atomic scale dimensions. However, the applications of metals and nitrides ALD in semiconductor device processes require a deeper understanding about the underlying deposition process as well as the physical and electrical properties of the deposited films. This article reviews the current research efforts in ALD for metal and nitride films as well as their applications in modern semiconductor device fabrication.

Atomic layer deposition of metal and nitride thin films: Current research efforts and applications for semiconductor device processing

High-power impulse magnetron sputtering (HiPIMS) is a promising sputtering-based ionized physical vapor deposition technique and is already making its way to industrial applications. The major difference between HiPIMS and conventional magnetron sputtering processes is the mode of operation. In HiPIMS the power is applied to the magnetron (target) in unipolar pulses at a low duty factor (<10%) and low frequency (<10 kHz) leading to peak target power densities of the order of several kilowatts per square centimeter while keeping the average target power density low enough to avoid magnetron overheating and target melting. These conditions result in the generation of a highly dense plasma discharge, where a large fraction of the sputtered material is ionized and thereby providing new and added means for the synthesis of tailor-made thin films. In this review, the features distinguishing HiPIMS from other deposition methods will be addressed in detail along with how they influence the deposition conditions, such as the plasma parameters and the sputtered material, as well as the resulting thin film properties, such as microstructure, phase formation, and chemical composition. General trends will be established in conjunction to industrially relevant material systems to present this emerging technology to the interested reader.

/pdf/an-introduction-to-thin-film-processing-using-high-power-3apigz7rif.pdf

An introduction to thin film processing using high-power impulse magnetron sputtering

High power pulsed magnetron sputtering: Fundamentals and applications

The authors present direct evidence for Te segregation to the grain boundaries in chalcogenide Ge2Sb2Te5 films by using transmission electron microscopy scans with a 0.5nm diameter focused probe. This finding is consistent with the observed impeded grain growth and with the post-transition relief of a “spikelike” stress, fully to the pretransition level. Te motion shows up in void formation below 200°C, a pileup of Te at the surface and its loss at higher (above 400°C) temperatures. Tuning the driving force for this segregation may be key for the optimal phase-change material design.

Evidence for segregation of Te in Ge2Sb2Te5 films: Effect on the “phase-change” stress

We demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes a large decrease in the resistance of thin films and a complete stress relaxation in films that were intrinsically compressively stressed. 100 nm beta tantalum thin films with intrinsic stresses of 2.0×1010 dynes/cm2 (tensile) to −2.3×1010 dynes/cm2 (compressive) were deposited onto thermally oxidized (100) silicon wafers by evaporation or dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured at 10 °C/min up to 850 °C in purified helium. Upon heating, the main stress mechanisms were elastic deformation at low temperature, plastic deformation at moderate temperatures and stress relief because of the beta‐to‐alpha phase transition at high temperatures. The temperature ranges over which the elastic and plastic deformation and the beta‐to‐alpha phase transition occurred varied with deposition pressure and substrate biasing. Incomplete compressive stress relaxation at high temperatures was observed if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800 °C due to substrate biasing during the deposition. We conclude that the main stress relief mechanism for tantalum films with intrinsic compressive stresses to completely relax their stress is the beta‐to‐alpha phase transition, while for intrinsically tensile films, this transformation has a much smaller effect on the stress.

The relationship between deposition conditions, the beta to alpha phase transformation, and stress relaxation in tantalum thin films

We demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes complete stress relaxation and a large decrease in the resistance of tantalum thin films. 100 nm beta tantalum thin films were deposited onto thermally oxidized silicon wafers by dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured during temperature-ramped annealing in purified He. Upon heating, films that were initially compressively stressed showed increasing compressive stress due to thermo-elastic deformation from 25 to 550°C, slight stress relief due to plastic deformation from 550 to 700°C and complete stress relief due to the beta to alpha phase transformation at approximately 700–800°C. Incomplete compressive stress relaxation was observed at high temperatures if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800°C. This incomplete beta to alpha phase transition was most commonly observed on samples that had radio frequency substrate bias greater than -100 V. We conclude that the main stress relief mechanism for tantalum thin films is the beta to alpha phase transformation that occurs at 700 to 800°C.

A. Mutscheller

Papers

The relationship between deposition conditions, the beta to alpha phase transformation, and stress relaxation in tantalum thin films

Effect of Deposition Conditions on Intrinsic Stress, Phase Transformation and Stress Relaxation in Tantalum Thin Films