J. Leon Shohet

Electron‐density and energy distributions in a planar inductively coupled discharge

Electron‐density and electron energy distribution functions (EEDFs) are measured in a 20‐cm‐diam by 14‐cm‐long cylindrical, inductively coupled plasma source driven by fields from a planar, spiral coil at 13.6 MHz. Radio‐frequency (rf) ‐filtered Langmuir probes are used to obtain spatial profiles of electron population characteristics in argon at powers and pressures of interest for etching and plasma‐assisted deposition (1–100 mT). Electron densities range from 1010 to 1012 cm3 with 100–500 W of rf power and peak on axis in the center of the cylindrical volume. The EEDFs show that the observed average electron energy varies by 1–2 eV spatially, with the highest values of average energy occurring at those regions of strongest rf electric field. The EEDF measurements also reveal a significant population of cold electrons trapped in a potential well at the location of peak electron density. From these spatial measurements, spatial estimates of conductivity and ionization rate are deduced.

Silicon oxide deposition in an electron cyclotron resonance plasma with microwave spectroscopic monitoring of SiO

A 2.45 GHz electron cyclotron resonance reactor was used to deposit silicon oxide films using both tetraethoxysilane (TEOS)/O2 and silane/O2. The reactor is equipped with an in situ microwave spectrometer in the frequency range 75–110 GHz, that is used to monitor the gas phase chemical species in this environment. The J=1→2 rotational transition of the vibrational ground state of silicon monoxide (SiO) was detected and monitored in plasmas of both gas mixtures. The integrated intensity of the microwave transition was used to obtain absolute densities of SiO integrated along the path length for both of these plasma chemistries. Silicon oxide films were deposited at pressures of a few mTorr and at low wafer temperature. The properties of the deposited films were characterized using infrared absorption and wet etch rate. The refractive indices of the films were measured by using multicolor ellipsometry. Deposition rates were determined as a function of oxygen/TEOS or oxygen/silane flow ratio. An inverse corr...

Real-time determination of plasma etch-rate selectivity

Real-time etch-rate selectivity of thin transparent films is determined within seconds by an in situ two-colour laser interferometer. Two-point laser reflectrometry is used to determine the etch rates and etch selectivity of unpatterned polysilicon and films. The state of a magnetically confined inductively coupled plasma tool used in the experiments, including rf power to the antenna and the wafer stage, gas pressure and flow rates, is computer controlled and monitored. The dependence of the etch selectivity on tool state parameters is characterized in real time by varying the tool state and monitoring the etch rate of the films. The etch rate measurements have been combined with density characterization of the etch radicals in the discharge. The time-dependent density of atomic chlorine during the process is obtained by temporal optical-emission actinometry combined with in-line mass spectrometry from a pressure calibrated residual gas analyser. The etch selectivity of polysilicon to in a chlorine discharge, determined by a simultaneous etch of both films, differs from the etch-rate ratios of the films when they are etched separately. It is suggested that this difference is due to the presence of oxygen in the polysilicon etch process when the two films are etched simultaneously.

Scatterometry for post-etch polysilicon gate metrology

The use of scatterometry as a rapid and non-destructive technique for the characterization of grating structures has received significant attention in recent years. The problems of mask alignment, overlay, latent image monitoring, and others have been investigate using scatterometry. Research is currently underway at TI which extends the state of the art by using scatterometry for the measurement of very small dimension gate-level polysilicon gratings on a thin oxide under-layer. The measurements were taken after etch and cleanup on typical process development test wafers used at TI and were acquired using a Bio-Rad CDS-2 scatterometer. A variety of gratin pitches and grating line widths were measured and compared to duplicate measurements obtained from top-down SEM. A total of 2,975 non-repeated measurements were collected on each metrology tool. The large range of line width result in overlapping measurements for each pitch, so linearity with pitch can be evaluated. The results from the scatterometer are in excellent agreement with the SEM in nearly all cases. For certain line widths, regardless of the grating pitch, a discrepancy can be seen between the measurement for the scatterometer and the SEM. The reason for this is currently under investigation. If side wall angle is treat as a fixed parameter, the discrepancies are removed. Example measurements and corresponding theoretical traces will ge shown for process development samples measured at TI. Some result from an extended gauge study will also be shown to provide estimates of the precision of the scatterometric measurements.

Effect of water uptake on the fracture behavior of low-k organosilicate glass

Water uptake in porous low-k dielectrics has become a significant challenge for both back-end-of-the-line integration and circuit reliability. This work examines the effects of water uptake on the fracture behavior of nanoporous low-k organosilicate glass. By using annealing dehydration and humidity conditioning, the roles of different water types and their concentrations are analyzed in detail. For as-deposited SiCOH films, annealing dehydration can enhance the resistance to crack occurrence, and these enhancements can be offset by higher humidity conditioning. It was found that the film-cracking threshold can be lowered by in-diffused water in the film as well as by water at the SiCOH/subtract interface. This occurs because the water decreases the film fracture energy and adhesion energy, respectively. By conditioning at high humidity, the variation of the film cracking threshold agrees well with the behavior of the film hardness and modulus of elasticity as a function of relative humidity. The crack mo...

Time-dependent dielectric breakdown measurements of porous organosilicate glass using mercury and solid metal probes

Time-dependent dielectric breakdown (TDDB) is one of the major concerns for low-k dielectric materials. During plasma processing, low-k dielectrics are subjected to vacuum ultraviolet photon radiation and charged-particle bombardment. To examine the change of TDDB properties, time-to-breakdown measurements are made to porous SiCOH before and after plasma exposure. Significant discrepancies between mercury and solid-metal probes are observed and have been shown to be attributed to mercury diffusion into the dielectric porosities.

Plasma-Generated OH Radical Production for Analyzing Three-Dimensional Structure in Protein Therapeutics

Protein three-dimensional structure dynamically changes in solution depending on the presence of ligands and interacting proteins. Methods for detecting these changes in protein conformation include ‘protein footprinting,’ using mass spectrometry. We describe herein a new technique, PLIMB (Plasma Induced Modification of Biomolecules), that generates µs bursts of hydroxyl radicals from water, to measure changes in protein structure via altered solvent accessibility of amino acid side chains. PLIMB was first benchmarked with model compounds, and then applied to a biological problem, i.e., ligand (EGF) induced changes in the conformation of the external (ecto) domain of Epidermal Growth Factor Receptor (EGFR). Regions in which oxidation decreased upon adding EGF fall along the dimerization interface, consistent with models derived from crystal structures. These results demonstrate that plasma-generated hydroxyl radicals from water can be used to map protein conformational changes, and provide a readily accessible means of studying protein structure in solution.

Atomic absorption spectroscopic measurements of silicon atom concentrations in electron cyclotron resonance silicon oxide deposition plasmas

The silicon atom densities in both silane/oxygen and tetraethoxysilane (TEOS)/oxygen electron cyclotron resonance (ECR) plasmas were measured as functions of microwave power, pressure, and gas flow rates. An atomic absorption spectrometer with a Si hollow-cathode lamp was constructed for these measurements. Silicon atom densities in silane/oxygen ECR discharges increase with rising plasma density, and a strong correlation was found between the Si atom gas-phase abundance and the silicon oxide film deposition rate. The measured Si concentrations [(1–7)×1010 cm−3] were high enough to account for a significant part of the film growth in the silane based chemistry. In TEOS/O2 discharges Si atom concentrations were lower by an order of magnitude, so Si is probably not a major contributor to the growth rate in that case. The internal temperature of Si atoms was found to vary from 380 to 720 K with increasing microwave power (200–650 W).

Fluorophore-based sensor for oxygen radicals in processing plasmas

A high concentration of radicals is present in many processing plasmas, which affects the processing conditions and the properties of materials exposed to the plasma. Determining the types and concentrations of free radicals present in the plasma is critical in order to determine their effects on the materials being processed. Current methods for detecting free radicals in a plasma require multiple expensive and bulky instruments, complex setups, and often, modifications to the plasma reactor. This work presents a simple technique that detects reactive-oxygen radicals incident on a surface from a plasma. The measurements are made using a fluorophore dye that is commonly used in biological and cellular systems for assay labeling in liquids. Using fluorometric analysis, it was found that the fluorophore reacts with oxygen radicals incident from the plasma, which is indicated by degradation of its fluorescence. As plasma power was increased, the quenching of the fluorescence significantly increased. Both immobilized and nonimmobilized fluorophore dyes were used and the results indicate that both states function effectively under vacuum conditions. The reaction mechanism is very similar to that of the liquid dye.

Extrinsic time-dependent dielectric breakdown of low-k organosilicate thin films from vacuum-ultraviolet irradiation

In this work, the effect of vacuum ultraviolet (VUV) photon irradiation on the time-dependent dielectric breakdown (TDDB) of low-k organosilicate thin films was investigated, with particular emphasis on extrinsic TDDB (includes Cu migration effects). State-of-the-art low-k a-SiOC:H thin films were utilized because of their relevance as both an interlayer dielectric and as a candidate Cu capping-layer material. Synchrotron radiation was used to mimic VUV photon irradiation from processing plasmas without the presence of charged particles. TDDB characteristic lifetimes of the low-k a-SiOC:H dielectrics, before and after VUV photon exposure, were measured based on a Ti/a-SiOC:H/Cu metal-insulator-metal structure. The deterioration of extrinsic TDDB was observed in the film after exposure to VUV photons with 9 eV energy. The most notable degradation of the dielectric characteristic lifetime was found when the Cu electrode was used as an anode in the sample after 9.0 eV VUV photon exposure (photon fluence is 4...