S. M. Sze

Reliability characteristics of NiSi nanocrystals embedded in oxide and nitride layers for nonvolatile memory application

The authors provided the reliability characteristics of nonvolatile nickel-silicide nanocrystal memories embedded in oxide and nitride layers for next-generation nonvolatile memory application. The charge trapping layer was deposited by sputtering a commixed target in the argon and oxygen/nitrogen ambiances, and then using a low temperature rapid thermal annealing to form nanocrystals. Transmission electron microscope clearly shows the sharpness and the density of nanocrystals. These proposed memory structures were compared for the charge storage ability, retention, and endurance. In addition, we used a simple simulation of electric field for nonvolatile nanocrystals memory to explain the advantages by using the high-k dielectric.

An implementation of parallel dynamic load balancing for adaptive computing in VLSI device simulation

Abstract.We present a new parallel semiconductor device simulation using the dynamic load balancing approach. This semiconductor device simulation based on the adaptive finite volume method with a posteriori error estimation has been developed and successfully implemented on a 16-PC Linux cluster with a message passing interface library. A constructive monotone iterative technique is also applied for solution of the system of nonlinear algebraic equations. Two different parallel versions of the algorithm to perform a complete device simulation are proposed. The first is a dynamic parallel domain decomposition approach, and the second is a parallel current-voltage characteristic points simulation. This implementation shows that a well-designed load balancing simulation can significantly reduce the execution time up to an order of magnitude. Compared with the measured data, numerical results on various submicron VLSI devices are presented, to show the accuracy and efficiency of the method.

The effects of plasma treatment for low dielectric constant hydrogen silsesquioxane (HSQ)

Abstract Low density materials, such as hydrogen silsesquioxane (HSQ), can offer lower dielectric constants. With HSQ, a low value of K can be achieved if the density of Si H bonding is maintained at a high level and the formation of –OH bonds and absorption or creation of water in the film is minimized. In this work, we have studied the use of hydrogen plasma to improve the quality of HSQ. In addition, the effects of N 2 and O 2 plasma post-treatments on HSQ are investigated. The leakage current of HSQ decreases as the H 2 plasma treatment time is increased. However, the leakage current of HSQ increases as the N 2 and O 2 plasma treatment time is increased. A model is proposed to explain the role of hydrogen in HSQ. The hydrogen passivates the surface of porous HSQ. The H 2 plasma treatment provides additional hydrogen passivation of the HSQ. On the other hand, the N 2 and O 2 plasma treatments reduce the hydrogen passivation of HSQ. As a result, both the leakage current and dielectric constant increase as the N 2 and O 2 plasma treatment time is increased. Finally, HSQ with H 2 plasma treatment is used as the intermetal dielectric in a multilevel interconnection structure. Consistent with our model, the via resistance decreases with increasing H 2 plasma treatment time.

Computer simulation of electron energy levels for different shape InAs/GaAs semiconductor quantum dots

Abstract A computational technique for the energy levels calculation of an electron confined by a 3D InAs quantum dot (QD) embedded in GaAs semiconductor matrix is presented. Based on the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, a finite height hard-wall 3D confinement potential, and the Ben Daniel–Duke boundary conditions, the problem is formulated and solved for the disk, ellipsoid, and conical-shaped InAs/GaAs QDs. To calculate the ground state and first excited state energy levels, the nonlinear 3D Schrodinger is solved with a developed nonlinear iterative algorithm to obtain the final self-consistent solutions. In the iteration loops, the Schrodinger equation is discretized with a nonuniform mesh finite difference method, and the corresponding matrix eigenvalue problem is solved with the balanced and shifted QR method. The proposed computational method has a monotonically convergent property for all simulation cases. The computed results show that for different quantum dot shapes, the parabolic band approximation is applicable only for relatively large dot volume. For the first excited states the non-parabolicity effect also has been found to be stronger than it at ground state. The QD model and numerical method presented here provide a novel way to calculate the energy levels of QD and it is also useful to clarify principal dependencies of QD energy states on material band parameter and QDs size for various QD shapes.

Memory characteristics of Co nanocrystal memory device with HfO2 as blocking oxide

In this letter, the Co nanocrystals using SiO2 and HfO2 as the tunneling and the control dielectric with memory effect has been fabricated. A significant memory effect was observed through the electrical measurements. Under the low voltage operation of 5V, the memory window was estimated to ∼1V. The retention characteristics were tested to be robust. Also, the endurance of the memory device was not degraded up to 106 write/erase cycles. The processing of the structure is compatible with the current manufacturing technology of semiconductor industry.

A Novel Nanowire Channel Poly-Si TFT Functioning as Transistor and Nonvolatile SONOS Memory

In this letter, a polycrystalline silicon thin-film transistor consisting of silicon-oxide-nitride-oxide-silicon (SONOS) stack gate dielectric and nanowire (NW) channels was investigated for the applications of transistor and nonvolatile memory. The proposed device, which is named as NW SONOS-TFT, has superior electrical characteristics of transistor, including a higher drain current, a smaller threshold voltage (Vth) , and a steeper subthreshold slope. Moreover, the NW SONOS-TFT also can exhibit high program/erase efficiency under adequate bias operation. The duality of both transistor and memory device for the NW SONOS-TFT can be attributed to the trigate structure and channel corner effect.

Nickel nanocrystals with HfO2 blocking oxide for nonvolatile memory application

A distributed charge storage with Ni nanocrystals embedded in the SiO2 and HfO2 layer has been fabricated in this study. The mean size and aerial density of the Ni nanocrystals are estimated to be about 5nm and 3.9×1012∕cm2, respectively. The nonvolatile memory device with Ni nanocrystals exhibits 1V threshold voltage shift under 4V write operation. The device has a long retention time with a small charge lose rate. Besides, the endurance of the memory device is not degraded up to 106 write/erase cycles.

The novel improvement of low dielectric constant methylsilsesquioxane by N2O plasma treatment

The organic silsesquioxane, methylsilsesquioxane (MSQ), has a low dielectric constant because of its lower film density compared to thermal oxide. However, the quality of MSQ film is degraded by the damage of oxygen plasma and hygroscopic behavior during photoresist stripping. In this work, we studied the N 2 O plasma treatment for improving the quality of MSQ. The leakage current of MSQ decreases as the N 2 O plasma treatment time is increased. The dielectric constant of N 2 O plasma-treated sample remains constant (∼2.7). In addition, the thermal stability of MSQ film can be enhanced. The role of N 2 O plasma is to convert the surface layer of organic MSQ into inorganic type by decomposition of the alkyl group and thus form a passivation layer. The inert passivation layer enhances the resistance to moisture uptake and O 2 plasma attack. Therefore, N 2 O plasma-treatment greatly improves the quality of low k MSQ film and removes the issue of photoresist stripping in the integrated process.

Eliminating dielectric degradation of low-k organosilicate glass by trimethylchlorosilane treatment

The interaction between low-k organosilicate glass (OSG) and photoresist removal is investigated. O2 plasma ashing and chemical wet stripper are commonly performed to remove photoresist (PR) in integrated circuit fabrication. However, O2 plasma or wet stripper will attack function groups and cause Si–OH group formation in OSG film during PR removal processing. The Si–OH groups often lead to moisture uptake and consequently dielectric degradation will occur in OSG film. Trimethylchlorosilane (TMCS) treatment can negate the damage in the OSG film after the PR removal process. In addition, chemical TMCS can react with Si–OH groups and reduces moisture uptake so that the dielectric characteristic of OSG can be maintained. Hence, TMCS treatment is a promising method for photoresist removal.

Improvement in Integration Issues for Organic Low-k Hybrid-Organic-Siloxane-Polymer

The organic low-k hybrid-organic-siloxane-polymer (HOSP®) has been investigated as an intermetal dielectric. The presence of Si-H and Si-CH 3 bonds instead of partial Si-O bonds lowers the dielectric constant compared to conventional siloxane-based spin-on glass. However, dielectric degradation occurs due to the destruction of functional groups in HOSP during the photoresist ashing process. In this work, we have applied NH 3 plasma nitridation to improve the quality of HOSP films. The NH 3 plasma process converts the organic HOSP surface into an inorganic surface by formation of a thin inert SiN x passivation layer. The inert layer can enhance the resistance of the HOSP film to moisture uptake and O 2 plasma attack during photoresist stripping. In addition it effectively prevents copper from penetrating the HOSP film.