Shahid Rauf

Inter-Strata Connection Characteristics and Signal Transmission in Three-Dimensional (3D) Integration Technology

In a general case of 3D integrated circuit (IC) technology, it is desirable to design a die for 3D integration with flexibility to facilitate integration with a number of other circuit dies. We present a generic circuit technique which minimizes power consumption and circuit area while allowing reliable signal transfer between 3D dies as well as enabling the design of a bonded interface circuitry without a complete knowledge of inter-strata connection configurations. We also present parasitic RC characteristics of inter-strata connection elements, such as micro-bumps and through-substrate vias, and discuss the technology scaling trends. An inter-strata signal transmission, according to our method, has receive and transmit circuitry with programmable power supply which can be independently controlled for achieving optimum power and signal drive. In addition, the receive circuitry includes hysteresis to allow superior signal integrity in the presence of inter-strata parasitic variations

A molecular dynamics investigation of fluorocarbon based layer-by-layer etching of silicon and SiO2

A molecular dynamics model is used to understand the layer-by-layer etching of Si and SiO2 using fluorocarbon and Ar+ ions. In these two-step etch processes, a nanometer-scale fluorocarbon passivation layer is grown on the material’s surface using low energy CFx+ ions or radicals. The top layers of the material are then reactive ion etched by Ar+ ions utilizing the fluorocarbon already present on the material surface. By repeating these two steps, Si or SiO2 can be etched with nanometer-scale precision and the etch rate is considerably faster than what traditional atomic layer etching techniques provide. The modeling results show that fluorocarbon passivation films can be grown in a self-limiting manner on both Si and SiO2 using low energy CF2+ and CF3+ ions. The fluorocarbon passivation layer is a few angstroms thick, and its thickness increases with the fluorocarbon ion’s energy. Increasing the ion energy, however, amorphizes the top atomic layers of the material. In addition, the fluorocarbon film beco...

A molecular dynamics model for the interaction of energetic ions with SiOCH low-κ dielectric

A molecular dynamics model is used to investigate the interaction of energetic ions with fluorocarbon passivated Si, O, C, and H (SiOCH) based low-κ dielectrics. The model includes a set of interatomic potentials required for the SiOCH–CFx interaction system, where the two- and three-body pseudopotentials have either been obtained from published literature or computed using ab initio techniques. The test structure used for the ion interaction simulations is put together through deposition of low energy SiOx+, CHy+, and H+ ions on a crystalline Si substrate. A thin fluorocarbon passivation layer is grown on the low-κ test structures by bombarding them with moderate energy CFx+ ions. Simulations of CF2+ ion interaction with the fluorocarbon passivated SiOCH samples show that the sputter yield of sample constituents (Si, O, and H) increases with ion energy and peaks at about 60°. H sputters more easily compared to other species, and the surface layer is expected to become H deficient over time. Sputtered H a...

Molecular-dynamics model of energetic fluorocarbon-ion bombardment on SiO2 I. Basic model and CF2+-ion etch characterization

A molecular-dynamics-based model has been developed to understand etching of amorphous SiO2, with and without a fluorocarbon reactive layer, by energetic fluorocarbon (CFx+) ions. The model includes a representation of the solid and a set of interatomic potentials required for the SiO2–CFx interaction system. Two- and three-body pseudopotentials have either been obtained from published literature or computed using ab initio techniques. The Stillinger–Weber potential construct is used to represent potentials in our model and particle trajectories are advanced using the velocity-Verlet algorithm. The model is validated by comparing computed bond lengths and energies with published experimental results. Computed yield for Ar+ ion sputtering of SiO2 is also compared with published data. In the computational results described in this article, the model SiO2 test structure (with a thin fluorocarbon reactive layer) is prepared by starting with α-quartz ([001] orientation) and bombarding it with 50-eV CF2+ ions. ...

Interstratum Connection Design Considerations for Cost-Effective 3-D System Integration

Emerging 3-D multistrata system integration offers the capability for high density interstratum interconnects that have short lengths and low parasitics. However, 3-D integration is only one way to accomplish system integration and it must compete against established system integration options such as system-on-a-chip (SoC) and system-in-a-package. We discuss multiple tradeoffs that need to be carefully considered for choosing 3-D integration over other integration schemes. The first step toward enabling 3-D design is characterizing the new interstratum connection elements, microconnects and through-Si vias, in a bonded 3-D technology. We have used both analytical- and simulation-based approaches to analyze the parasitic characteristics of interstratum connections between bonded 3-D stratum, and have compared the interstratum power and performance with SoC global interconnects, taking into account the impact of technology scaling. The specific elements in an interstratum connection and their electrical properties strongly depend on the choice of 3-D integration architecture, such as face-to-face, back-to-face, or the presence of redistribution layer for bonding. We present an adaptive interstratum IO circuit technique to drive various types of interstratum connections and thus enable 3-D die reuse across multiple 3-D chips. The 3-D die/intellectual property reuse concept with the adaptive interstratum IO design can be applied to design 3-D ready dice to amortize additional 3-D costs associated with strata design, test, and bonding process.

Model for nitridation of nanoscale SiO2 thin films in pulsed inductively coupled N2 plasma

As nitration of SiO2 gate dielectric can increase the film’s dielectric constant and reduce boron penetration into the Si channel during ion implantation, plasma nitridation is of considerable interest for the fabrication of semiconductor devices. A coupled plasma equipment-surface physics model is used in conjunction with an experimental analysis of nitrided SiO2 thin films to understand the mechanism of SiO2 plasma nitridation. This investigation is conducted in a pulsed inductively coupled N2 plasma. Computational results show that N atoms and N2+ ions are the primary species in the N2 plasma that contribute to the nitridation of SiO2 thin film. N atoms adsorb at the SiO2 surface and diffuse into the bulk film, and most nitrogen near the surface is due to these adsorbed N atoms. N2+ ions, on the other hand, penetrate deeper into the SiO2 film in an ion-implantation-like manner, and these ions are responsible for the observed tail in the nitrogen concentration profile. Nitrogen concentration in the film...

Molecular-dynamics model of energetic fluorocarbon-ion bombardment on SiO2. II. CFx+ (x=1, 2, 3) ion etch characterization

A molecular-dynamics-based model has been used to understand etching of SiO2, with and without a fluorocarbon-polymer layer, by energetic fluorocarbon (CFx+) ions. The test structures for computational experiments are prepared by starting with α-quartz ([001] orientation) and bombarding it with low-energy ions: Ar+ ion for amorphous and fluorocarbon ions for fluorocarbon-polymerized test structures. CF+, CF2+, and CF3+ ions with a range of energies and angles of impact are then bombarded on these test structures to characterize fluorocarbon-ion etching. Results show that aggregate Si and O etch yields increase with ion energy for all ions and all angles of impact. Etch yields, however, exhibit nonlinear dependence on angle of impact with a peak around 60°. This nonlinear behavior is attributed to the balance among the incident ion energy transfer fraction, depth of energy deposition, and cluster scattering direction during secondary scattering events. The Si etch yield increases going from CF+ to CF2+ and...

Computational modeling of process induced damage during plasma clean

When partially completed circuits come in contact with plasmas during integrated circuit fabrication, current from the plasma can potentially damage active devices on the wafer. A suite of computational models is used in this article to investigate damage to ultrathin (1.0–5.5nm) transistor gate dielectric (SiO2) during Ar∕O2 based plasma cleaning in a capacitively coupled plasma reactor. This modeling infrastructure includes a two-dimensional plasma equipment model for relating process control parameters to ion and electron currents, a three-dimensional model for flux density calculation within a circular via, an electrostatic model for computing potential across the gate dielectric, and a percolation model to investigate dielectric damage characteristics. Computational results show that when the plasma current comes in contact with the gate dielectric, the gate dielectric rapidly charges up and the potential difference across the dielectric saturates at the level necessary to support the plasma induced ...

Simulations of magnetized capacitively coupled plasmas operating at constant power and voltage

The impact of frequency, magnetic field and secondary electron emission on the characteristics of a magnetized capacitively coupled Ar/C2F6 plasma operating at constant power is investigated. The plasma characteristics at constant power are also compared to corresponding results for constant voltage operation. Some plasma characteristics behave similarly in the two modes of operation. For example, charged species densities increase as a function of frequency in both modes. However, unlike for constant voltage operation, charged and neutral species densities decrease with the application of a magnetic field in the constant power mode at high frequencies and at sufficiently large magnetic fields. This uncharacteristic behaviour is attributed to a substantial increase in negative ion power consumption in Ar/C2F6 when a strong magnetic field is applied. Application of the magnetic field decreases electron mobility towards the sheaths, which increases the participation of negative ions in sheath and pre-sheath dynamics. Negative ions consequently shift closer to the electrodes, negative ion power consumption increases substantially, and relatively less power is left for the electrons. Lower electron power results in the production of less charged and neutral species through electron impact processes. Simulations in Ar confirm that, without the negative ions, charged and neutral species densities increase with the application of a magnetic field at constant power. Also, for small magnetic fields, species densities increase with the magnetic field even in electronegative plasma discharges.

Fluorocarbon based layer-by-layer etching of Si and SiO/sub 2/ - A molecular dynamics investigation

Summary form only given. As the critical dimensions in microelectronics devices shrink below 20 nm, it is becoming essential to control plasma etching processes on a sub-nm scale. Although atomic layer etching (ALE) techniques provide such dimensional precision, ALE etch rates are slow enough to be impractical for commercial applications. In this paper, we use a molecular dynamics (MD) model to investigate layer-by-layer etching of SiO2 and Si using low to moderate energy fluorocarbon and Ar+ ions. The following process sequence is examined: a. Deposition of a thin fluorocarbon layer on the material surface using low energy CF2 + or CF3 + ions, b. Use of Ar+ ions to remove a material layer whose thickness is commensurate with the F on the surface. As the fluorocarbon passivation layer will be a few Aring thick, it is expected that more than one atomic layer will be etched during each step and the surface might become rough on an atomic scale. The goal is not ALE per se but layer-by-layer etching of the material in a manner that dimensions can be controlled on a sub-nm scale. Characteristics of the fluorocarbon passivation layer are examined in this paper, and the role on Ar+ ion energy on etching properties is investigated. The computational MD model used in the present study has been described in detail in [V.V. Smirnov, et al., J. Appl. Phys. 97, 093302 (2005)]. This MD model takes into account the interactions between Si, O, C and F. In the model, the pseudo-potentials for 2 and 3-body interactions have either been obtained from the literature or computed using ab-initio techniques utilizing Gaussian98. The Stillinger-Weber potential construct has been used to represent the pseudo-potentials and the velocity-Verlet algorithm is used to advance particle trajectories. Following ion impact, material temperature is controlled using the Berendsen thermal bath model. Computations show that the fluorocarbon passivation layer is a few Aring thick, its thickness increases with fluorocarbon ion energy, and CF2 + ions produce a thicker layer than CF3 + ions. When Ar+ ions with energy less than 50 eV are bombarded on SiO2, SiO2 is etched only as long as F is available near the surface for reactive ion etching