A computer code for the simulation of ion beam irradiation of nanostructures has been developed. The code simulates the transport of energetic ions through matter by means of a Monte Carlo algorithm, similar to the often-used TRIM code (Ziegler et al. (1985) [1]). New effects occur compared to bulk, when irradiating nanostructures, which are of the same size as the ion range or the damage cascade. To account for these effects, the target in our code does not consist of layers like in TRIM but can be defined as an arbitrary 3-dimensional structure. This allows to obtain more accurate 3D distributions of implanted ions and implantation damage for nanostructures, which cannot be described by a stack of layers. We demonstrate the functionality of the code by comparing simulations with ion beam implantation into nanowires.

Ion beam irradiation of nanostructures – A 3D Monte Carlo simulation code

Front end process simulation is an invaluable tool in assessing current and future process options. This review describes the application of process simulation in modeling geometry, doping and stress effects in advanced logic processes. Continuum and atomistic approaches, both necessary to capture the physics involved with the most advanced options, are discussed. Also detailed are advancements in numerical techniques which enable the efficient and robust simulation necessary to keep pace with technology development.

Process modeling for advanced device technologies

Ionenstrahlimplantation ist eine nutzliche und weit verbreitete Methode um Materialien zu dotieren. Nanostrukturen verhalten sich unter Ionenbestrahlung oft deutlich anders als das entsprechende Volumenmaterial; zum Beispiel unterscheiden sich die erzeugten Dotierprofile sowie die Erzeugung und das Ausheilen von Defekten. In der vorliegenden Arbeit wird dieses Unterschiedliche Verhalten unter Ionenbestrahlung von drei Gesichtspunkten aus untersucht: Im ersten Teil wird ein neu entwickeltes Computerprogramm zur Simulation der Ionenbestrahlung von Nanostrukturen vorgestellt und diskutiert. Ahnlich wie bei vergleichbaren Programmen wird dabei ein Monte-Carlo-Algorithmus in Kombination mit der Zweierstos-Naherung verwendet. Im Gegensatz zu konventionellen Programmen wird das Target aber durch kleine Zellen und nicht durch Schichten reprasentiert, so dass sich beliebige Nanostrukturen dreidimensional abbilden lassen. Die erzielten Simulationsergebnisse stimmen gut mit experimentellen Befunden uberein. Im zweiten Teil der Arbeit wird die ionenstrahlinduzierte Verbiegung von Nanodrahten untersucht. Je nach Energie der Ionen lassen sich die Nanodrahte in verschiedene Richtungen verbiegen und ausrichten. Als zugrundeliegender Mechanismus wird die inhomogene Verteilung verschiedener ionenstrahlinduzierter Defekte identifiziert. Der dritte Teil beschaftigt sich mit der Dotierung von GaAs-Nanodrahten mittels Mangan. Wegen der geringen Loslichkeit der Ubergangsmetalle in III-V-Halbleitern kann das Mangan nicht beim Wachstum der Nanodrahte eingebracht werden. Es wird gezeigt, dass die Mangan-Dotierung von GaAs mittels Ionenstrahlimplantation moglich ist. Dabei ist eine erhohte Implantationstemperatur erforderlich, um das in Nanodrahten ohnehin verstarkte dynamische Ausheilen noch weiter zu unterstutzen und die Kristallinitat der Nanodrahte zu erhalten. Alle drei Teile zeigen deutliche Unterschiede bei der Ionenbestrahlung von Nanodrahten im Vergleich zum Volumenmaterial.

Ion-Solid Interaction in Semiconductor Nanowires

We present a parallelization method based on message passing interface (MPI) for a Monte Carlo program for two-dimensional (2-D) and three-dimensional (3-D) simulation of ion implantations. We use a master-slave strategy where the master process synchronizes the slaves and performs the input-output operations, while the slaves perform the physical simulation. For this method the simulation domain is geometrically distributed among several CPU's which have to exchange only very little information during the simulation. Thereby, the communication overhead between the CPU's is kept so low that it has almost no influence on the performance gain even if a standard network of workstations is used instead of a massively parallel computer to perform the simulation. We have optimized the performance gain by identifying bottlenecks of this strategy when it is applied to arbitrary geometries consisting of various materials. This requires the application of different physical models within the simulation domain and makes it impossible to determine a reasonable domain distribution before starting the simulation. Due to a feedback between master and slaves by online performance measurements, we obtain an almost linear performance gain on a cluster of workstations with just slightly varying processor loads. Besides the increase in performance, the parallelization method also achieves a distribution of the required memory. This allows 3-D simulations on a cluster of workstations, where each single machines would not have enough memory to perform the simulation on its own.

Parallelization of a Monte Carlo ion implantation simulator

Nanostructures and nanomaterials with their meso-scopic properties, which can be integrated into functional devices, will enable a variety of new applications in future. They can be grown with specific properties by plenty of physical and chemical methods, and subsequent modification using ion irradiation significantly expands the potpourri of functionality of this important material class. As the ion range becomes comparable to the size of the small structures, important effects must be considered in experimental planning: reduced incorporation of implanted species, morphological changes induced by point defects, as well as strongly enhanced dynamic annealing and sputtering.

Low Energy Ion Beam Modification of Nanostructures

A new physically based Monte Carlo ion implantation simulator has been developed and implemented in UT-MARLOWE The new simulator is capable of simulating 2-D and 3-D implants into arbitrary topography with multiple layers, both crystalline and amorphous Emphasis has been placed on computational efficiency, and improvements over previous simulators ranging from 1-3 orders of magnitude in CPU time have been observed The accuracy of the simulation is observed not to be compromised by the algorithms for improved computational efficiency

Monte Carlo simulation of ion implantation into topographically complex structures

The rapid progress of CMOS process technology has led to increased process complexity and fabrication cost and has created a strong need for accurate and computationally efficient ion implantation models. In this paper, we propose new and improved analytic models for as-implanted impurity and damage profiles in one and two dimensions. The development of models for the as-implanted damage profile is becoming increasingly important, since it is well known that the implant-induced damage has a significant impact on the diffusion of impurities during subsequent thermal treatment, especially under minimal thermal budget conditions. A new approach to 2-D analytic ion implant simulation that takes into account implant-induced damage, and generates 2-D interstitial/vacancy profiles in addition to impurity profiles, is also described. Finally, a methodology is discussed for automating the extraction of model parameters for generating lookup tables.

G. Balamurugan

Papers

Monte Carlo simulation of ion implantation into topographically complex structures

New analytic models and efficient parameter extraction for computationally efficient 1-D and 2-D ion implantation modeling