Ivan L. Berry

Predicting synergy in atomic layer etching

Atomic layer etching (ALE) is a multistep process used today in manufacturing for removing ultrathin layers of material. In this article, the authors report on ALE of Si, Ge, C, W, GaN, and SiO2 using a directional (anisotropic) plasma-enhanced approach. The authors analyze these systems by defining an “ALE synergy” parameter which quantifies the degree to which a process approaches the ideal ALE regime. This parameter is inspired by the ion-neutral synergy concept introduced in the 1979 paper by Coburn and Winters [J. Appl. Phys. 50, 5 (1979)]. ALE synergy is related to the energetics of underlying surface interactions and is understood in terms of energy criteria for the energy barriers involved in the reactions. Synergistic behavior is observed for all of the systems studied, with each exhibiting behavior unique to the reactant–material combination. By systematically studying atomic layer etching of a group of materials, the authors show that ALE synergy scales with the surface binding energy of the bu...

Effects of resist strip and clean on USJ performance

As junction depths decrease below 50 Aring, surface conditions before, during and after implantation have an increasing impact on the characteristics of the junction. Understanding the effects of photoresist strip and clean on the junction characteristics after annealing are critical to achieve expected and consistent device performance. Photoresist strip and clean is found to cause: junction etching, dopant bleaching and junction oxidation. Implant conditions can enhance these effects. Surprisingly, the strip and clean can also effect the dopant distribution, and possibly dopant activation. These effects are modified and many times enhanced by degree of amorphization, and vary significantly by type of activation anneal. Details of a parametric study show influence of resist strip parameters (power, pressure, temperature, chemistry) on surface oxidation, surface etching and surface passivation, as well unexpected interactions between the resist strip with the implant and anneal conditions.

Applying sputtering theory to directional atomic layer etching

Plasma assisted atomic layer etching (ALE) has recently been introduced into manufacturing of 10 nm logic devices. This implementation of ALE is called directional ALE because ions transfer momentum to the etching surface during the removal step. Plasma assisted directional ALE can be described as sputtering of a thin modified layer on the surface of the unmodified material. In this paper, the authors introduce a collision cascade based Monte Carlo model based on sputtering theory which has evolved for over 50 years [P. Sigmund, Thin Solid Films 520, 6031 (2012)]. To test the validity of this approach, calculated near threshold argon ion sputtering yields of silicon and chlorinated silicon are compared to published experimental data. The calculated ALE curve for Cl2/Ar ALE of tantalum is in good agreement with the experiment. The model was used to predict the presence of salient sputtering effects such as ion mass and impact angle dependence, as well as redeposition in directional ALE. Finally, the author...

Ion Beam Patterning of High-Density STT-RAM Devices

Dependence on ion beam energy, ion species, and incidence angles is investigated to reduce sidewall re-deposition on the magnetic tunnel junction barrier. Experimental and simulated etch data, for a representative spin-torque transfer random access memory structure with 40 nm critical dimension and 150 nm pitch, indicated a reduction in the sidewall re-deposition when operating at: high angle, high voltage, and with Xe as the source gas. The Monte Carlo binary collision model simulations showed re-deposition thickness reduced by ~75% with Xe versus Ar at 1 kV beam energy and 30° incidence angle.

Ultra shallow junction (USJ) formation using plasma assisted doping on 3D devices structures

Advanced inductively coupled plasma techniques and surface treatments have been used to demonstrate 5nm conformal shallow junctions at low energy with no silicon structure damage. N-type PH3 plasma assisted doping was characterized by dopant diffusion and electrical activation with increasing wafer temperature. Plasma assisted doping at high wafer temperature showed no structure damage even at a high incident energy condition with a bias power applied to the wafer, while a shallow junction of less than 7nm of Xj formation was achieved with low incident energy condition without bias power. Adding a silicon surface modification step when using the decoupled plasma condition prior to PH3 doping was found to enhance the dopant level and lower Rs dramatically. Various annealing techniques were compared to understand the impact to dopant activation and levels to form shallow junctions of less than 7nm.

Formation of 5 nm Ultra Shallow Junction on 3D Devices Structures by Ion Energy Decoupled Plasma Doping

Advanced inductively coupled plasma techniques and surface treatments have been used to demonstrate 5 nm conformal shallow junctions at low energy with no silicon structure damage. N-type PH3 plasma-assisted doping was characterized by dopant diffusion and electrical activation with increasing wafer temperature. Plasma-assisted doping at high wafer temperature showed no structure damage even at a high incident energy condition with a bias power applied to the wafer, while a shallow junction of less than 5 nm of Xj formation was achieved with low incident energy condition without bias power. Adding a silicon surface modification step when using the decoupled plasma condition prior to PH3 doping was found to enhance the dopant level and lower Rs dramatically. Various annealing techniques were compared to understand the impact to dopant activation and levels to form shallow junctions of less than 5 nm.