Phillip J. Stout

Inductively Coupled Pulsed Plasmas in the Presence of Synchronous Pulsed Substrate Bias for Robust, Reliable, and Fine Conductor Etching

Inductively coupled pulsed plasmas in the presence of synchronous pulsed substrate bias are characterized in a commercial plasma etching reactor for conductor etching. The synchronous pulsed plasma characteristics are evaluated through the following: 1) Ar-based Langmuir probe diagnostics; 2) Ar/Cl2 plasma modeling utilizing the hybrid plasma equipment model and the Monte Carlo feature model for the investigation of feature profile evolutions; 3) basic etching characteristics such as average etch rate and uniformity; 4) sub-50-nm Dynamic Random Access Memory (DRAM) basic etching performance and profile control; and 5) charge damage evaluation. It is demonstrated that one can control the etching uniformity and profile in advanced gate etching, and reduce the leakage current by varying the synchronous pulsed plasma parameters. Moreover, it is shown that synchronous pulsing has the promise of significantly reducing the electron shading effects compared with source pulsing mode and continuous-wave mode. The synchronous pulsed plasma paves the way to a wider window of operating conditions, which allows new plasma etching processes to address the large number of challenges emerging in the 45-nm and below technologies.

Monte Carlo simulation of surface kinetics during plasma enhanced chemical vapor deposition of SiO2 using oxygen/tetraethoxysilane chemistry

Tetraethoxysilane/oxygen (TEOS/O2) chemistries are now used for low plasma enhanced chemical vapor deposition (PECVD) of SiO2 when high conformality and low temperature are required. The surface processes leading to film growth, carbon elimination, and conformality are not well characterized. We have developed a model to investigate the surface kinetics of the PECVD of SiO2 films using TEOS/O2 chemistry. The model includes precursor adsorption and desorption, densification of the film, void formation, pyrolysis, plasma surface interactions, and geometric shadowing. Results for growth rate, fraction of carbon retained in the film, film conformality, and film roughness are discussed.

Modeling of high power semiconductor switches operated in the nonlinear mode

Although optically activated high power photoconductive semiconductor switches (PCSS) are usually triggered using uniform illumination, under select conditions they can be activated and closed in <1 ns with a spot of light near the contacts. This observation requires free carriers to either travel at speeds faster than their saturation velocity or for there to be a carrier generation mechanism that propagates with similar speeds. A two‐dimensional time‐dependent computer model of a GaAs high power switch has been employed to investigate these observations, and activation of PCSS by spots of light in particular. Results from the model suggest that the transport of band‐to‐band recombination radiation plays an important role in propagating electrons across the switch when the switch is closed with a spatially nonuniform laser pulse. Reabsorption of the recombination radiation and photogeneration of carriers is a mechanism which generates free carriers in the gap between the contacts at speeds greater than saturation velocity. The results also indicate that the switch is sensitive to the location of the activating laser pulse. Less laser fluence is required to close the switch if illumination occurs near the cathode rather than near the anode.

Recouping etch rates in pulsed inductively coupled plasmas

Pulsed rf plasmas are increasingly being employed for plasma etching at future technological nodes. Although the plasma uniformity usually improves with pulsing, the lower time-averaged power decreases the etch rate and the lower throughput is undesirable. It is therefore important to evaluate different strategies to restore higher etch rates while retaining the advantages of pulsed plasmas. In this work, the impact of varying pulsing modes in an inductively coupled plasma on plasma characteristics and feature profile evolution are discussed using the results from a two-dimensional reactor scale plasma model coupled to a Monte Carlo based feature profile model. Results are discussed for poly-Si etching in an Ar/Cl2 gas mixture. The consequences of source-only and bias-only pulsing modes on discharge characteristics, ion energy distributions (IEDs) to the wafer, and feature profile evolution are discussed. Although the etch depth rates were found to be higher for source-only pulsing compared to the synchro...

Decreasing high ion energy during transition in pulsed inductively coupled plasmas

Pulsed RF plasmas sustained in electronegative gas mixtures are increasingly being employed for plasma etching at future technological nodes. During the plasma transition from the afterglow to the active-glow, ion energies at the wafer can substantially increase due to the high voltage required to deposit bias power into few electrons. These high energy ions, albeit few, increase the possibility of ion bombardment damage and are, therefore, detrimental to the etching process. Strategies to decrease the high ion energies during transition are investigated using a two-dimensional computational plasma model. Results for poly-Si etch in an Ar/Cl2 gas mixture indicate that the high ion energies can be reduced by offsetting the bias pulse from the source pulse with minimal impact on the etch depth rates.

Modeling surface kinetics and morphology during 3C, 2H, 4H, and 6H–SiC (111) step-flow growth

A Monte Carlo surface kinetics model has been developed to predict growth rate, morphology, and the atomic content of thin films of various SiC polytypes (3C, 2H, 4H, 6H). The model represents the crystal lattice on a structured mesh which retains fixed atom positions and bond partners indicative of a perfect crystal lattice. Specified events occurring at different rates and probabilities change the configuration and the atomic content of the lattice. Events in the model include precursor transport to surface, adatom adsorption, diffusion, and desorption from surface, growth and etching reactions between adatoms and lattice atoms, and evaporation. The initial validation of the model for SiC consists of replicating trends seen when experimentally growing polytypes of SiC (111) on circular mesas and on off-axis vicinal planes. The model can predict the (111) plane faceting seen in β-SiC and the hexagonal structures seen when growing on α-SiC. Also, step flow growth rates which change with flow direction are...

Comparing ionized physical vapor deposition and high power magnetron copper seed deposition

A computational modeling comparison is made between ionized physical vapor deposition (IPVD) and high power magnetron (HPM) deposition of copper. For the comparison the point of view of the feature scale is stressed where the two reactors are distinguishable by the magnitude and ratio of specie (Cu,Cua,Cu+,Ar+) flux, the angular distribution of the specie, and the energy of the ions incident on the feature surface. The HPM is characterized for the conditions studied by a metal flux content made up almost entirely of copper athermals, an Ar+ ion flux about four times the Cu metal flux, decreasing Cu+ fraction and increasing Cu athermal flux to surface with increasing target power, and both no sputter and sputter regimes at the wafer possible. The IPVD reactor is characterized for the conditions studied by a Cu metal flux with a large neutral fraction but significant ions and athermals, an Ar+ ion flux on the order of the Cu metal flux, and only a sputter regime at the wafer possible. An increase in target ...

Modeling dual inlaid feature construction

Dual inlaid construction of copper interconnect structures involves a sequence of tightly coupled plasma processes with subtle variations in one process impacting subsequent processes. An integrated plasma reactor/feature physics based modeling suite has been applied to three-dimensional (3D) dual inlaid (DI) feature construction. Specifically, the goal of this article is to understand process interdependencies during DI construction. The DI feature is used in inlaid copper interconnects to define metal lines and their connection to the metal layer below. One advantage of the DI feature is only one metallization step (barrier deposition/seed deposition/electroplating/chemical mechanical polish) is required to deposit metal into both the metal lines and the via connections to the metal layer below. Discussed will be the 3D feature modeling of fluorocarbon plasma etching of vias and trenches in SiO2 to construct dual inlaid features. The model includes 11 steps in the dual inlaid construction process. Papay...

Modeling high power magnetron copper seed deposition: Effect of feature geometry on coverage

The deposition of copper using a high power magnetron (HPM) has been studied using reactor and feature scale models. Discussed are results for Cu seed HPM deposition on trench, via, and dual inlaid features with different geometries (aspect ratio and side wall angles). At low wafer powers the Cu seed feature coverage is characterized by geometric shadowing due to the broad angular distribution of the dominant Cu athermal. At high wafer powers the metal deposited at feature bottom is sputtered by Ar+ and redistributed to the side walls. The deposition rate within a feature is nonlinear with time as metal deposited at the feature opening obstructs incoming metal from reaching the inside of the feature. Competing trends of higher copper flux at wafer center versus edge and higher Ar+ flux at wafer center versus edge result in a transition of the field thickness heights from edge>center at low wafer powers to center

Plasma and process characterization of high power magnetron physical vapor deposition with integrated plasma equipment—feature profile model

High power magnetron physical vapor deposition (HPM-PVD) has recently emerged for metal deposition into deep submicron features in state of the art integrated circuit fabrication. However, the plasma characteristics and process mechanism are not well known. An integrated plasma equipment-feature profile modeling infrastructure has therefore been developed for HPM-PVD deposition, and it has been applied to simulating copper seed deposition with an Ar background gas for damascene metalization. The equipment scale model is based on the hybrid plasma equipment model [M. Grapperhaus et al., J. Appl. Phys. 83, 35 (1998); J. Lu and M. J. Kushner, ibid., 89, 878 (2001)], which couples a three-dimensional Monte Carlo sputtering module within a two-dimensional fluid model. The plasma kinetics of thermalized, athermal, and ionized metals and the contributions of these species in feature deposition are resolved. A Monte Carlo technique is used to derive the angular distribution of athermal metals. Simulations show th...