AVS1996 Session PS2-MoM: Deposition I - PECVD

Monday, October 14, 1996 8:20 AM in Room 201B

Monday Morning

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8:20 AM		PS2-MoM-1 Plasma Properties and Gas Phase Reactions in Inductively-Coupled High Density Plasma Chemical Vapor Deposition W. Collison, H. Nguyen, B. McMillin, A. Demos, M. Barnes (Lam Research Corporation); M. Kushner (University of Illinois, Urbana-Champaign) Inductively coupled plasma sources are being developed to address the need for high plasma density (>10\super 10\/cm\super 3\), low pressure (a few to 10s mTorr) etching of semiconductor materials. These sources are also capable of depositing high quality SiO\sub 2\ thin films by plasma-enhanced chemical vapor deposition. The plasma properties and gas phase reactions in these high density plasma chemical vapor deposition (HDP-CVD) reactors are some of the essential factors in determining the quality of SiO\sub 2\ films. In this work, inductively-coupled HDP-CVD of SiO\sub 2\ films from SiH\sub 4\/O\sub 2\/Ar mixtures are studied theoretically and experimentally to understand some fundamental physical and chemical processes. The theoretical work is done by using the two-dimensional Hybrid Plasma Equipment Model (HPEM). The effects of ICP power, chamber pressure, gas mixture (especially the ratio of SiH\sub 4\/O\sub 2\) and chamber geometry (aspect ratio, nozzle position, etc.) on plasma properties (including plasma density distribution, plasma potential distribution, ion and neutral density distribution, radical fluxes to wafer, etc.) and gas phase reactions are studied in detail. Also, the effects of different sticking coefficients and reaction rates are investigated. The results of theoretical work are compared with experimental results. We found that the densities of SiH\sub 3\ and SiH\sub 2\O in gas phase have a direct relation with the deposition rate. From the comparison, we can understand how the quality of SiO\sub 2\ film is affected by process parameters (such as ICP power, pressure, etc.) and chamber characteristics.
8:40 AM		PS2-MoM-2 DSMC Simulation of Reactor Feature Scale Flows M. Hudson, T. Bartel, A. Russo (Sandia National Laboratories); T. Cale (Arizona State University) The Sandia massively parallel Direct Simulation Monte Carlo (DSMC) chemically reacting particle code was used to model the rarefied flow around multiple features on a wafer. The flow near the surface of a wafer is rarefied because the size of the features are much less than the mean free path of the flow. At this scale, traditional Navier-Stokes continuum analyses are not applicable. The DSMC particle technique properly models the free-molecular to continuum flow regimes which occur at the feature, meso, and reactor scales. Thus, the DSMC technique allows the near-surface reactor flow to be coupled with the features in a single reactor feature scale model (RFSM). We will present results showing the effects of feature density, aspect ratio, and surface chemistry on the concentrations and fluxes to the surface of a wafer. The angular and energy distribution of each incident species will also be examined for varying reactor operating conditions. Two-dimensional flow around multiple patterns of four 0.5 micrometer high features were computed with the DSMC-RFSM and compared with a flat surface. The computational space extended 3 mean free paths (mfp=1 cm at 5 mtorr and 300 K) above the surface. The surface chemistry addressed both etching and deposition. Different surface reactions were specified on vertical and horizontal surfaces with different sticking coefficients. For a Ar/SiH4/O2 gas flow, the surface reaction was SiH4+O2-->SiO2+2H2 with 0.1 to 0.9 reaction probability. The DSMC-RFSM allows us to identify and understand the interactions between the physical phenomena which occur at the reactor, meso, and feature scales in a single model. Also, more accurate etch and deposition rates should result from topography models using the boundary conditions provided by the DSMC-RFSM.
9:00 AM		PS2-MoM-3 Reactivity Measurements of SiH in the Deposition of a-Si:H from Silane and Disilane Plasmas using Plasma Enhanced Chemical Vapor Deposition G. Barker, E. Fisher, P. McCurdy (Colorado State University) Hydrogenated amorphous silicon (a-Si:H) is currently used in the development of many electronic devices. Intense research has shown that the material properties of a-Si:H are highly dependent on the deposition parameters. The parameters for plasma enhanced chemical vapor deposition include source gas, gas dilution, rf power, and time of deposition. The goal of our research is to assist in the elucidation of the chemistry involved in the deposition of a-Si:H. Deposition studies have been performed using silane and disilane as the source gas in a 13.56 MHz inductively coupled plasma reactor. The deposition rate decreases with increasing hydrogen dilution. Microstructure quality is seen to improve with increasing hydrogen dilution as well as with increasing rf power. Surface reactivity studies on the SiH radical in silane and hydrogen-diluted silane plasmas have shown the radical's reactivity to be near unity. The measurements were made with the Imaging of Radicals Interacting with Surfaces (IRIS) technique. The IRIS technique combines molecular beam technology with spatially resolved laser-induced fluorescence (LIF) to directly determine radical reactivities during the deposition process. In addition, we have performed substrate temperature dependence measurements for SiH from SiH\sub 4\ and SiH\sub 4\/H\sub 2\ plasmas. We find that for a wide range of substrate temperatures (300-600 K), the reactivity of SiH does not change appreciably. Preliminary results for SiH from a disilane plasma will also be presented.
9:20 AM		PS2-MoM-4 A Growth Model for the Fast Deposition of a-Si:H R. Severens, J. Bastiaanssen, M. Sanden, D. Schram (Eindhoven University of Technology, The Netherlands) Results on the fast deposition of a-Si:H using an expanding thermal plasma are presented. The substrate temperature was varied from 100 up to 350 \super o\C while the plasma conditions were kept constant at I\sub arc\=45 A, Ar/H\sub 2\/SiH\sub 4\=55/10/10 scc/s and chamber pressure 0.18 mbar. Hydrogen content [H] was measured using infrared absorption spectrometry, growth rate is determined using in situ ellipsometry. Urbach energy E\sub u\ and density of states at midgap DOS using dual beam photoconductivity absorption spectroscopy. Slit experiments are performed to establish the sticking probability of the depositing radical. [H], E\sub u\ and DOS decrease with increasing substrate temperature. The values for the best sample deposited at the highest temperature of 350 \super o\C are: [H] = 7%, E\sub u\ = 48 meV and DOS = 5x10\super 15\ cm\ super -3\. The growth rate is around 7 nm/s and independent of substrate temperature. The results are explained on the basis of a kinetic growth model. It is assumed that the SiH\sub 3\ radical is the dominant radical for growth. SiH\sub 3\ is first physisorbed on the hydrogenated a-Si:H growth surface. Growth sites, i.e. dangling bonds, are created either by means of hydrogen abstraction by the surface diffusing physisorbed SiH3 radical to form SiH\sub 4\ or by thermal desorption of H\sub 2\. The latter process is stronger for higher substrate temperatures. The growth occurs by the chemisorption of the SiH\sub 3\ radical on a dangling bond. It is postulated that the DOS is proportional to the density of dangling bonds present on the growth surface. Since thermal desorption is larger for higher substrate temperatures it is essential that the growth rate is large (> 1 nm/s) when the substrate temperature is high (> 300 \super o\C). The reason is that the number of dangling bonds on the growth surface otherwise would be high, which would result in a higher DOS. Hydrogen incorporation in this simple model occurs when the SiH\sub 3\ is chemisorbed. The chemisorption releases 2.2 eV which is available for the direct desorption of H\sub 2\. The latter effect could explain the observed small activation energy for hydrogen incorporation. The model also predicts a growth rate which does not depend on the substrate temperature.
9:40 AM		PS2-MoM-5 Influence of Gas Phase Species on Silicon Oxide Film Properties for Films Deposited using ECR TEOS + O\sub 2\ and Silane + O\sub 2\ Plasmas K. Chew, E. Augustyniak, R. Woods, J. Shohet (University of Wisconsin, Madison) A 2.45 GHz electron cyclotron resonance (ECR) reactor, using both silane + O\sub 2\ and tetraethoxysilane (TEOS) + O\sub 2\, was used to investigate the influence of many gas phase species that are present during silicon oxide deposition on the deposited film properties. The gas phase species were monitored using microwave spectroscopy, optical emission spectroscopy, and Si atomic absorption techniques. The film quality was characterized using infrared absorption, wet etch rate, multicolor ellipsometry, and ESCA and compared to thermal oxide film. In SiH\sub 4\ based deposition, the silicon oxide film quality approaches that of thermal oxide for films deposited using O\sub 2\/SiH\sub 4\ ratios higher than 1 at 500 W and a pressure of 5.0 mTorr. Also at this pressure and power, no O or OH emission was detected for O\sub 2\/SiH\sub 4\ ratios lower than 1, while no SiH emission was detected for O\sub 2\/SiH\sub 4\ ratios higher than 1. A strong correlation was found between Si atom abundance and deposition rate, as well as film quality. Under similar deposition conditions with TEOS + O\sub 2\, the silicon oxide film quality approaches thermal oxide film quality for O\sub 2\/TEOS ratio higher than 3. The carbon content in the film is less than 1.0 atomic % for those silicon oxide films deposited with O\sub 2\/TEOS ratio higher than 3. A strong O emission intensity correlated with high film quality for both SiH4 + O\sub 2\ and TEOS + O\sub 2\ plasmas deposition. *This work was supported by the NSF under Grant No. EEC-8721545. Generous donations of equipment were made by Hewlett-Packard Co., Schumacher Co., and ASTeX Corp.
10:00 AM		PS2-MoM-6 A Study of the Mechanisms of Deposition of SiO\sub 2\ by PECVD of Alkoxysilanes K. Bogart, E. Fisher (Colorado State University) Plasma enhanced chemical vapor deposition (PECVD) of thin films is used extensively in the microelectronics industry during the manufacture of integrated circuits. The mechanism by which thin films are formed on a substrate is not well understood. As device geometries continue to decrease, understanding the interactions of precursor molecules with the surface of the film during deposition becomes critical to ensure a high quality film. Direct measurements of the surface reactivity of radical species during the deposition of a thin film will aid in the elucidation of the chemistry occurring at the surface of the depositing film. Direct measurements of radical surface reactivities can be made using the Imaging of Radicals Interacting with Surfaces (IRIS) technique, which combines molecular beam technology with spatially resolved laser induced fluorescence. We have investigated the reactivity of the OH radical in water and alkoxysilane plasmas, such as tetraethoxysilane (TEOS), which are used to deposit SiO\sub 2\. The presence of hydroxyl groups in a SiO\sub 2\ thin film is indicative of a poor quality film. The reactivity of the OH radical with the surface during plasma processing may be indicative of how the hydroxyl groups are incorporated into the film. The reactivity of OH from a water plasma on a silicon surface at 300 K with native oxide has been determined to be ~0.5. This value correlates well with previous results of OH from a water plasma on a silicon nitride surface.\super 1\ The reactivity of the OH radical in 100% TEOS and 20% TEOS/80% O\sub 2\ plasmas on Si/SiO\sub 2\ substrates will be presented. OH has been observed in the 20% TEOS/80% O\sub 2\ plasma in small quantities, with a preliminary reactivity value of ~0.5. OH radicals produced from an oxygen plasma used to etch SiO\sub 2\ films deposited from alkoxysilanes will also be discussed. Composition and trends in deposition parameters for films deposited from alkoxysilane plasmas will also be presented. 1. Fisher, et al. J. Phys. Chem., 97, (1993), p10287.
10:20 AM		PS2-MoM-7 Microwave Spectroscopic Measurements of Oxidation Products in TEOS/Oxygen ECR Silicon Oxide Deposition Plasmas R. Woods, E. Augustyniak, K. Chew, J. Shohet (University of Wisconsin, Madison) Microwave spectroscopy in the 75-110 GHz range was applied to seven carbon-containing species (and to SiO) in O\sub 2\+TEOS (tetraethoxysilane) silicon oxide deposition plasmas. The determined concentrations correlate with carbon incorporation into the oxide films. The high density, low pressure plasmas were created in a 2.45 GHz electron cyclotron resonance (ECR) reactor. Fractional absorptions as low as 10\super -6\ could be measured, corresponding to molecule densities in the range 10\super 9\ - 10\super 10\ cm\super -3\. The diagnostic was used to monitor C\sub 2\H\sub 5\OH, CH\sub 3\CHO, CH\sub 2\CO, CH\sub 3\OH, H\sub 2\CO, HCOOH, and CH\sub 3\CCH as functions of power (30-800 W), pressure (3-40 mTorr), O\sub 2\/TEOS ratio (1-8) and total O\sub 2\+TEOS flow rate (5-50 sccm). These species correspond to stable molecule intermediate products in the sequential oxidation of the ethoxy fragments from TEOS. Qualitatively all detected molecules followed the same pattern; their concentrations increased with pressure and decreased with plasma power. Densities of larger molecules decreased with power faster than those of smaller ones. The strongest absorption was due to formaldehyde, whose density was measurable up to 800 W, while other species fell below their detection thresholds in the 100-400 W range. It appears that the oxidative destruction of the organic fragments of TEOS is very extensive at the higher power used in industrial microelectronics applications. \super *\This work was supported by the NSF under Grant No. EEC-8721545. Most of the microwave spectrometer was donated by Hewlett-Packard Co. and the TEOS temperature controller was donated by Schumacher Co.
10:40 AM		PS2-MoM-8 Atomic Absorption Measurements of Silicon in ECR Oxide Deposition Plasmas E. Augustyniak, K. Chew, J. Shohet, R. Woods (University of Wisconsin, Madison) An atomic absorption diagnostic for measurement of silicon atom concentrations in O\sub 2\+SiH\sub 4\ silicon oxide deposition plasmas was developed using a Si hollow-cathode lamp source. Attenuation measurements of the six Si I resonance lines 4s \super 3\P\super o\ - 3p\super 2\ \super 3\P (250.69 - 252.85 nm) permitted independent determination of the populations of the three sublevels (J = 0, 1, 2) of the ground state. The high density, low pressure plasmas were created in a 2.45 GHz electron cyclotron resonance (ECR) reactor. Concentrations were measured as a function of pressure (3-30 mTorr), power (200-650 W), O\sub 2\/SiH\sub 4\ ratio (0.5-6), and total O\sub 2\+SiH\sub 4\ flow rate (5-60 sccm). Silicon atom concentration increased with power and silane flow rate. The highest measured Si density was near 10\super 11\ cm\super -3\ at 650 W, 5 mTorr, 20 sccm of SiH\sub 4\, and 20 sccm of O\sub 2\. The Si concentrations were strongly correlated with deposition rates and the quality of the silicon oxide films. The fine-structure sublevels of the \super 3\P ground state were populated according to a Boltzmann distribution. The internal temperature, determined from relative intensities, varied from 380K (200 W) to 720K (650 W). Inferred Si atom fluxes were high enough to account for the observed silicon oxide deposition rates. Thus neutral Si atoms can be considered as a candidate for the silicon dioxide film precursor in the silane/oxygen ECR plasma. In contrast, measurements in the TEOS+O\sub 2\ plasma have not revealed measurable amounts of Si atoms. \super *\This work was supported by the NSF under Grant No.EEC-8721545.
11:00 AM		PS2-MoM-9 Measurement of Ion Enhanced Deposition during PECVD of SiO/sub/2 using the Effect of Glass Substrates on Deposition Rate K. Sera, S. Ma, B. Shieh, J. McVittie (Stanford University) Previous test structure experiments and profile modeling results have indicated that ion bombardment enhances deposition rate during PECVD of SiO2. In addition, it is known that deposition rates decrease when a glass substrate is substituted for a conductive substrate such as a silicon wafer. In this work, we have used an on-wafer ion current probe to show that ion current is decreased by 20% on a glass substrate compared to a silicon wafer while the deposition rate decreased by 10%. In addition, by using overhang test structures, it was found that the neutral deposition component, as measured in shadowed regions, was not affect by the conductivity of the substrate. Using a linear combination model with ion driven and neutral driven components, it was found that all the model parameters except for a sticking coefficient and the ion distribution could be extracted from the observed rate and ion current differences. Assuming a cosine to the 10th power form for the ion angle distribution and fitting a single constant stick coefficient, the model, as use in our profile simulator (SPEEDIE), was able to correctly predict the observed profiles over a range of aspect ratios from 0.2 to 4.0.
11:20 AM		PS2-MoM-10 Electrical Properties of Plasma Fluorinated Silicon Oxide Films Deposited at Room Temperature K. Kim, Y. Song, J. Song, G. Lee (Lousiana State University) The electrical properties of fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at room temperature with disilane as silicon precursor were studied. The film deposition was made in conventional parallel plate plasma reactor by flowing 2 sccm of disilane, 100 sccm of nitrous oxide, and 20 sccm of tetrafluomethane. The film deposition rate was about 10 nm/min with<\+-\3% of thickness uniformity across the 4 inch diameter silicon wafers. Thermal stability of the films was monitored with the infrared transmission spectroscopy and the variation of peak wave numbers for Si-O, Si-F, and Si-OH bondings were carefully traced. The relative dielectric constant for the films was calculated to be 4.425. The high-frequency capacitance-voltage measurement gave an average flat band voltage shift of -0.123V for the MOS devices fabricated with these films, corresponding to 3.823 x 10\super 10\ cm\super -2\ of oxide fixed charge. It was also observed that the distribution of interface trap densities followed U-shape having a minimum value of 2.547 x 10\super 11\ cm\super -2\eV\super -1\ at 0.415 eV from the top of the valence band. The dielectric breakdown characteristics showed that no early failures at field values of \<=\ 3MV/cm were found and 79% of devices on the films had the breakdown field strength of 7 MV/cm and higher, resulting 7.11 MV/cm of the average measured dielectric breakdown field strength.
11:40 AM		PS2-MoM-11 Effect of Temperature on Plasma-induced Charging Damage in PECVD Processes J. O'Neill, C. Waskiewicz, D. Cote (IBM Microelectronics) Plasma-induced charging damage to thin oxides is a subject of increasing concern in integrated circuit manufacturing as gate dielectrics are scaled to thicknesses less than 100\Ao\. This oxide degradation is believed to result from traps and defects generated by Fowler-Nordheim tunneling currents induced within the dielectric. Temperature has long been known to play an important role in determining oxide lifetime through its effect on the rate of trap generation. This paper examines the effect of temperature on charge damage in the plasma enhanced chemical vapor deposition of phosphosilicate glass films (PECVD PSG) used for 64Mbit DRAM applications. Charge damage levels for PSG processes at temperatures between 350\super o\C and 500\super o\C were analyzed with antenna structures with ratios of 0.2M, 1M and 10M. The degradation of 100\Ao\ oxide films was characterized by leakage and time-dependent dielectric breakdown (TDDB) measurements. Both high frequency and quasistatic CV techniques were used to measure the trap density within thin oxides exposed to PSG processes at different temperatures. While the film properties and fill characteristics of PSG improve with increasing temperature, both the trap density and the level of charge damage increase significantly. Constant-current stressing of thin oxide capacitors at various stress temperatures was used to simulate dielectric degradation which occurs on antenna structures in the PECVD environment. These results are consistent with a mechanism for charging damage which is controlled by the generation tunneling-induced traps within the oxide . The implications of thermally enhanced charging damage in plasmas used for DRAM manufacturing are also discussed.