Erasmus Langer

Through Silicon Via Reliability

Vertical integration of diverse semiconductor technologies can be achieved by utilizing interconnections through entire silicon substrates, known as through silicon vias (TSVs). TSVs present an interesting case study for reliability evaluation, given the particular fabrication technologies, geometries, and potential failure modes associated with such structures. A specific TSV technology is introduced, and key parameters for reliability assessment, such as residual stress, resistance, leakage, and dielectric breakdown, are discussed. Reliability data are presented, including the characterization of TSV parameters as a function of various accelerated lifetime stress tests, as well as assessments of the density and impact of TSV manufacturing defects. The presented data demonstrate that while the TSV is inherently quite robust, latent manufacturing defects pose a significant risk to long-term reliability. Screening methodologies, defect modes, failure analysis methods, process improvement, and correspondingly improved defect density results are discussed. The results are considered pertinent to the development and reliability of novel 3-D integrated process technologies.

Numerical Analysis of Acoustic Wave Generation in Anisotropic Piezoelectric Materials

We present an “Ab Initio“ transient analysis of acoustic wave generation in piezoelectric materials which takes account of second order effects. The computer program we have developed for that purpose solves the fundamental differential equations in two space dimensions with the corresponding mechanical displacements and the electrical potential as dependent variables by a semi-implicit finite difference scheme rather than by wave approximations. This has become possible with acceptable usage of computer resources only by introducing a novel form of boundary conditions for the quasi infinite sagittal plane to avoid reflection phenomena. We present numerical results for YZ-LiNb03 and ST-Cut of Quartz.

Effects of Bosch scallops on metal layer stress of an open Through Silicon Via technology

Through Silicon Via (TSV) is a lead topic in interconnects and 3D integration research, mainly due to numerous anticipated advantages. However, several challenges must still be overcome if large scale production is to be achieved. In this work, we have studied effects of Bosch scallops concerning mechanical reliability for a specific TSV technology. The presence of scallops on the TSV wall modifies the stress distribution along the via. By means of Finite Element Method (FEM) simulations, we could assess this change and understand the process. The achieved results support experiments and give a better insight into the influence of scallops on the stress in an open TSV.

Parallelization of a Monte-Carlo ion implantation simulator for three-dimensional crystalline structures

The simulation of ion implantation using a Monte-Carlo method is one of the most time consuming tasks in process simulation, which makes it a first-order target for parallelization. We present a parallelization strategy for the Monte-Carlo ion implantation simulator MCIMPL based on the message passing interface (MPI), with an almost linear performance gain.

Parallelization of a Monte Carlo ion implantation simulator

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 CPUs which have to exchange only very little information during the simulation. Thereby, the communication overhead between the CPUs 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.

Three-dimensional process and device modeling

Abstract This contribution is intended to review the international state-of-the-art in three-dimensional process and device modeling. As one particular example, results for ion implantation into a three-dimensional trench are presented. Redistribution of dopants, interstitials and vacancies with fully coupled models is discussed. The recent refinements to carrier transport models in semiconductor devices are presented. As a particular example for three-dimensional device simulation the influence of the shape of the field-oxide in the width direction is discussed. Some remarks on the computational requirements are made.

Surface and Bulk Wave Velocities in Arbitrary Anisotropic Piezoelectric Materials

We present a numerical algorithm for the calculation of phase velocities of acoustic surface and bulk waves in anisotropic piezoelectric materials. The mathematical model is based on fundamental partial differential equations in three spatial dimensions which are the equations of motion and Poissons equation. We present examples for LiNb03 and Quartz.

Numerical analysis of acoustic wave generation in anisotropic piezoelectric materials

Abstract We present an ab initio transient analysis of acoustic wave generation in piezoelectric materials, which takes into account second-order effects ( e.g. , bulk wave generation and interaction between surface waves and bulk waves). The computer program we have developed for this purpose solves the fundamental differential equations in two space dimensions with the corresponding mechanical displacements and the electrical potential as dependent variables using a semi-implicit finite difference scheme rather than by wave approximations. This has become possible with acceptable usage of computer resources only by introducing a novel form of boundary conditions for the quasi-infinite sagittal plane to avoid reflection phenomena. We present numerical results for YX LiNbO 3 .

Stress evolution on tungsten thin-film of an open through silicon via technology

We have studied the stress evolution in the tungsten film of a particular open TSV technology during the thermal processing cycle. The film is attached to the vias wall and some plasticity is expected in the metal due to the temperature variation. Our work introduces a stress model for thin-films utilizing the traditional mechanical FEM approach. The results reveal potential reliability issues and a specific evolution of the stress in the tungsten layer.

Stress reduction induced by Bosch scallops on an open TSV technology

Through Silicon Via (TSV) is a lead topic in interconnects and 3D integration research, mainly due to numerous anticipated advantages. However, several challenges must still be overcome if large scale production is to be achieved. In this work, we have studied effects of Bosch scallops concerning mechanical reliability for a specific TSV technology. We identified that the presence of scallops on the TSV wall modifies the stress distribution. The achieved results support experiments and give a better insight into the influence of scallops in an open TSV.