Energetic ions during plasma-enhanced atomic layer deposition and their role in tailoring material properties

Abstract

Plasma-enhanced atomic layer deposition (PEALD) has obtained a prominent position in the synthesis of nanoscale films with precise growth control. Apart from the well-established contribution of highly reactive neutral radicals towards film growth in PEALD, the ions generated by the plasma can also play a significant role. In this work, we report on the measurements of ion energy and flux characteristics on grounded and biased substrates during plasma exposure to investigate their role in tailoring material properties. Insights from such measurements are essential toward understanding how a given PEALD process at different operating conditions can be influenced by energetic ions. Ion flux-energy distribution functions (IFEDFs) of reactive plasmas typically used for PEALD (O 2 , H 2 , N 2 ) were measured in a commercial 200 mm remote inductively coupled plasma ALD system equipped with RF substrate biasing. IFEDFs were obtained using a gridded retarding field energy analyzer and the effect of varying ICP power, pressure and bias conditions on the ion energy and flux characteristics of the three reactive plasmas were investigated. The properties of three material examples-TiO x , HfN x and SiN x -deposited using these plasmas were investigated on the basis of the energy and flux parameters derived from IFEDFs. Material properties were analyzed in terms of the total ion energy dose delivered to a growing film in every ALD cycle, which is a product of the mean ion energy, total ion flux and plasma exposure time. The properties responded differently to the ion energy dose depending on whether it was controlled with RF substrate biasing where ion energy was enhanced, or without any biasing where plasma exposure time was increased. This indicated that material properties were influenced by whether or not ion energies exceeded energy barriers related to physical atom displacement or activation of ion-induced chemical reactions during PEALD. Furthermore, once ion energies were enhanced beyond these threshold barriers with RF substrate biasing, material properties became a function of both the enhanced ion energy and the duration for which the ion energy was enhanced during plasma exposure. These results have led to a better insight into the relation between energetic ions and the ensuing material properties, e.g. by providing energy maps of material properties in terms of the ion energy dose during PEALD. It serves to demonstrate how the measurement and control of ion energy and flux characteristics during PEALD can provide a platform for synthesizing nanoscale films with the desired material properties.

Plasma-Assisted ALD of Highly Conductive HfNx: On the Effect of Energetic Ions on Film Microstructure

“…The ion flux-energy distribution functions (IFEDFs) of incident ions are measured using an Impedans Semion retarding field energy analyzer (RFEA) [31][32][33], as described in detail in Ref. [34]. As reported by Profijt et al, a mono-modal IFEDF for the grounded electrode (|V bias |= 0 V) condition, whereas the application of external RF substrate bias resulted in a bi-modal IFEDF [31].…”

“…Furthermore, the RFEA is also used to estimate the flux of incident ions using Γ i = I c e ⋅ A e , where I c is the collector current measured by the RFEA, e is the elementary charge and A e is the effective collector area. Ref [34]. describes a detailed procedure to deduce the value of factor A e , equal to (3.9 ± 1.0) 10 -3 cm 2 for the RFEA probe used in this work.…”

MOS Capacitance Measurements for PEALD TiO2 Dielectric Films Grown under Different Conditions and the Impact of Al2O3 Partial-Monolayer Insertion

“…The self-bias voltage varied by approximately 70-100 V during the 100-150 W O 2 plasma pulse. This voltage drop value in the plasma sheath (see Figure 1b) is sufficient to supply energy to the ions, to induce chemical reactions in growing film during PEALD [48].…”

Plasma deposition—Impact of ions in plasma enhanced chemical vapor deposition, plasma enhanced atomic layer deposition, and applications to area selective deposition

“…With the development of high-density low-pressure plasma sources in the 90 th , for which the energy of ions is controlled independently to the plasma production, many authors have studied the use of ions in PECVD processes [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] . More recently, it has also been suggested that one could also take advantage of ions in PEALD processes to optimize the physical properties of the layer under growth [23][24][25][26][27][28][29] .…”