Daniel L . Flamm | Massachusetts Institute of Technology (MIT) (original) (raw)

Papers by Daniel L . Flamm

Proceedings of SPIE, Apr 22, 1987

We present a low temperature (<300°C) plasma deposition process to prepare novel fluorine-cont... more We present a low temperature (<300°C) plasma deposition process to prepare novel fluorine-containing silicon nitride films (p-SiN:F1 using SiH4-NF-N2 discharge mixtures at 14 MHz RF applied frequency. The deposition rate can be extremely high, up to 1600 A/min. p-SiN:F has electrical properties (dielectric constant, breakdown strength, resistivity, etc.) which compare favorably with high temperature CVD silicon nitride. By controlling the feed chemistry and physical variables of the discharge, a wide variety of film compositions are achieved. Two classes of films were identified as stable or unstable to air exposure and the instability of the films correlated with the atom fraction of fluorine initially incorporated. The results obtained from IR, AES, and RBS measurements show that low hydrogen-containing films are produced by the introduction of fluorine in the silicon nitride films. More importantly, the concentration of Si-H is extremely low because strong Si-F bonding replaces relatively weak Si-H bonds that satisfy free Si orbitals in conventional plasma nitride, and the hydrogen remaining in the film is present as stable N-H bonds. We believe this substitution of silicon-bound hydrogen, caused by the gas phase and surface-driven reactions, is a reason for superior film properties. The mechanism for this novel discharge chemistry is discussed.

IEEE Transactions on Electrical Insulation, Apr 1, 1982

Low pressure plasmas of halogens, halocarbons, and their mixtures are in general use for etching ... more Low pressure plasmas of halogens, halocarbons, and their mixtures are in general use for etching micron-sized features on Si, GaAs, and InP. Several processing parameters may be varied to optimize plasma conditions for etching rates and profile control. Manipulation of substrate temperature, pressure, applied frequency and gas feed composition are discussed in detail and specific examples are presented to illustrate these effects on etching Si and III-V compounds.

Journal of Vacuum Science and Technology, Mar 1, 1982

Journal of Applied Physics, Jun 1, 1982

The homogeneous reaction between F or F2 and SiF2, the latter formed by the high-temperature reac... more The homogeneous reaction between F or F2 and SiF2, the latter formed by the high-temperature reaction of solid silicon with SiF4, is accompanied by an intense chemiluminescent ’’flame’’ with the spectrum previously observed during silicon etching by F and F2. This experiment provides direct confirmatory evidence that chemiluminescence from both reactions arises from the homogeneous reaction between SiF2 and fluorine atoms or molecules.

Journal of vacuum science & technology, May 1, 1990

As the lateral dimensions of ultra-large-scale integration (ULSI) circuit features approach a few... more As the lateral dimensions of ultra-large-scale integration (ULSI) circuit features approach a few-tenths of a micron, demands on the etch transfer of patterns into thin films become increasingly challenging. These demands, combined with the greater susceptibility to create damage, require that new methods are evaluated and compared for etching fine structures in order to establish processing technologies. Submicron polysilicon etching has been performed on a single-wafer etcher using two different sources that sustain intense discharges at low pressure (≲10−3 Torr). The first is an electron cyclotron resonance (ECR) source operated at 2.45 GHz. The second source is a simple helical resonator (HR) structure operated at radio frequencies (RF). The comparisons made between the two sources were the etched profiles of polysilicon, material selectivity, polysilicon etch rates, and etch uniformity. These preliminary experiments show that both systems have great promise to successfully pattern ULSI structures. The advantages and disadvantages of ECR and improved HR sources will be discussed.

Journal of The Electrochemical Society, Nov 1, 1982

Journal of vacuum science & technology, Apr 1, 1983

Plasma etching techniques for III-V compound semiconductors are reviewed, emphasizing design cons... more Plasma etching techniques for III-V compound semiconductors are reviewed, emphasizing design considerations in the choice of gases, discharge parameters, and substrate temperature. Mechanisms are proposed for anisotropic, isotropic, and crystallographic chemical etching. Applications of plasma etching in device fabrication are given.

Journal of Applied Physics, Aug 1, 1988

The copper-catalyzed fluorination of silicon is first order in [F2] and in [Cu]s until the covera... more The copper-catalyzed fluorination of silicon is first order in [F2] and in [Cu]s until the coverage reaches ∼4 monolayers. Above ∼4 monolayers the reaction rate is zero order in copper, suggesting a limited number of catalytically active Cu/Si sites. Copper islands form at high coverages, above saturation, and provide a reservoir of catalyst. The limited rate of surface diffusion of copper leads to anisotropic etching and feature size-dependent etch depths. The copper compounds, CuF2 and CuO, and copper silicides, Cu5Si and Cu3Si, all catalyzed the F2-Si reaction which suggests that they are all converted to the same active species. The results can be explained by mechanisms involving copper fluorides or copper silicides as active intermediates.

Applied Physics Letters, Apr 15, 1985

We find that gaseous ClF3 is an effective and selective etchant for a variety of transition metal... more We find that gaseous ClF3 is an effective and selective etchant for a variety of transition metals and metal compounds. Kinetics were studied for etching α-Ta (13–16 atom % N), Ta2N, and Ta2O5 in this gas, as a function of temperature and pressure, to provide effective activation energies of 4.0, 4.4, 7.7 kcal/mole, respectively. Relative etch rates measured in CF4/O2 and NF3 plasmas indicate that ClF3 gaseous etching has more than an order of magnitude better selectivity for nonoxidic metal compounds over the corresponding oxide. At 100 °C, selectivity for etching α-Ta or Ta2N over Ta2O5 is more than 160:1. Other materials used in semiconductor manufacture, such as SixNy, W, TaSi2, and photoresist, were also briefly surveyed and the results suggest ClF3 holds promise for isotropic etching applications that require high selectivity.

Chemischer Informationsdienst, Feb 9, 1982

This paper describes the deposition of dielectric silicon oxide from TEOS in helium/oxygen mixtur... more This paper describes the deposition of dielectric silicon oxide from TEOS in helium/oxygen mixtures in a parallel plate rf plasma reactor. Under appropriate process conditions, highly directional deposition of low-stress stoichiometric silicon oxide is achieved. The step coverage profiles and the chemical and physical properties of these Si02 films were studied to gain an understanding of t,he origin of preferentially vertical deposition. The typical deposition conditions used in this study were 1 torr total pressure, 320' C substrate temperature, 1-40% TEOS and 0-80% O2 in low power density (0.1-0.4 W/cm2) 14 MHz rf discharges. Step coverage, chemical stability and film stress were found to be most dependent on the 02:TEOS gas flow ratio. This dependence will be explained by the various effects involved in the oxide deposit ion mechanism.

MRS Proceedings, 1987

The copper catalyzed fluorination of silicon is first-order in [F 2 ] and in [Culs until the cove... more The copper catalyzed fluorination of silicon is first-order in [F 2 ] and in [Culs until the coverage reaches-4 monolayers. Above-4 monolayers the reaction rate is zero order in copper, suggesting a limited number of catalytically active Cu/Si sites. Surface diffusion of copper leads to decrease in the etch rate as a function of time as well as feature size-dependent etch depths. The copper compounds CuF 2 , CuO, and copper silicides, Cu 5 Si and Cu 3 Si all catalyzed the F 2-Si reaction which suggests that they are all converted to the same active species. The results can be explained by mechanisms involving copper fluorides or copper silicides as active intermediates.

MRS Proceedings, 1986

Etching of silicon by molecular fluorine is accelerated when trace quantities of copper are prese... more Etching of silicon by molecular fluorine is accelerated when trace quantities of copper are present on the surface. Copper is a residue formed when sputter-deposited aluminum (containing 0.5 % copper) is selectively removed by HF from the silicon surface. The temperature dependence of the etching rate was studied in the range 60–290°C. At temperatures higher than 80°C copper causes a ˜100-fold increase in the rate of etching of the underlying silicon (100), compared to unmetallized samples. Above 180°C, F2 exhibits a higher absolute etch rate than equivalent concentrations of fluorine atoms. Preliminary results for other metal contaminants and etchant gases indicate that silver also accelerates F2 etching, and copper enhances etching by NF3. The results are interpreted in terms of a catalytic mechanism.

MRS Proceedings, 1989

We have characterized the step coverage and film quality of (tetraethoxysilane) TEOSbased silicon... more We have characterized the step coverage and film quality of (tetraethoxysilane) TEOSbased silicon oxides which are directionally deposited on horizontal surfaces of trench features under oxygen-lean conditions in a high frequency (14 MHz) discharge. The film thickness on the sidewalls depends most strongly on the 02 :TEOS feed ratio. Water uptake after ambient exposure was used as a measure of film quality and the amount of water absorbed in the film correlated well with changes in the refractive index and stress. Oxide quality on horizontal surfaces could be improved by decreasing the TEOS feed or increasing the discharge power, but the sidewall oxide quality could not be improved by these methods. Small NF 3 additions to the discharge markedly improved sidewall quality, altered the angle between the sidewall and the bottom of trench features from 90" to-115' (tapered profile) and increased the deposition rate, while preserving the directionality of deposition.

ABSTRACT A description is given of the deposition of dielectric silicon oxide from TEOS in helium... more ABSTRACT A description is given of the deposition of dielectric silicon oxide from TEOS in helium/oxygen mixtures in a parallel-plate RF plasma reactor. Under appropriate process conditions, highly directional deposition of low-stress stoichiometric silicon oxide is achieved. The step coverage profiles and the chemical and physical properties of these SiO2 films were studied to gain an understanding of the origin of preferentially vertical deposition. The typical deposition conditions used in this study were 1 torr total pressure, 320°C substrate temperature, 1-40% TEOS, and 0-80% O2 in low-power-density (0.1-0.4 W/cm2) 14 MHz RF discharges. Step coverage, chemical stability and film stress were found to be most dependent on the O2:TEOS gas flow ratio. This dependence can be explained by the various effects involved in the oxide deposition mechanism

Journal of The Electrochemical Society, Apr 1, 1983

Monitoring optical emission has become a valuable tool for the plasma processing of semiconductor... more Monitoring optical emission has become a valuable tool for the plasma processing of semiconductor materials. We haveextended this technique by monitoring atomic emission from etch products excited in an auxiliary discharge located downstreamof the plasma ...

Proceedings of SPIE, Mar 15, 1989

ABSTRACT We have studied the chemical and physical properties of silicon oxide films plasma depos... more ABSTRACT We have studied the chemical and physical properties of silicon oxide films plasma deposited from TEOS (tetraethoxysilane), to gain an understanding of the origins of (1) step coverage and (2) film stability. TEOS was diluted in helium/oxygen mixtures and deposited as a function of discharge frequency (150 kHz and 14 MHz) and 02 flow in a parallel plate reactor. The typical deposition conditions were 1 torr total pressure, 320°C substrate temperature, 1 -9% TEOS, 1 -80% 02, and -0.1 W/cm2 discharge power. Films deposited at high frequency with excess oxygen were generally oxygen-rich, chemically unstable and hygroscopic, while films deposited at low frequency were stable to moisture and slightly deficient in oxygen. However, coverage profiles of high frequency films showed an unusual degree of directionality, which could be used to advantage for the coating of high aspect ratio features. We suggest that a judicious combination of high and low frequency discharges may improve film properties while maintaining directional step coverage. Isotopic labeling experiments were performed using 1802 to gain insight into the origins of the oxygen that is contained in these PECVD films. Complete isotopic scrambling was not observed. Film composition data suggest that there is one tenacious Si-0 bond which remains with the silicon from the original TEOS molecule during the reaction to form Si02.

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, May 1, 1987

Chemical and radiation-enhanced gas-solid etching of materials that are important in microelectro... more Chemical and radiation-enhanced gas-solid etching of materials that are important in microelectronics, fusion and space technologies, are compared and reviewed. Existing evidence suggests that the basic processes that drive spontaneous etching of several etchant-material combinations may be similar: F/Si, H/Si and H/C can be cited as examples. On the other hand, many etchant-material systems appear to involve system-specific processes that should not be generalized: examples are the XeF,/Si and Cl/Si systems. Experiments show that when chemical etching is the dominant phenomenon, energetic particle or photon ~mb~dm~t generally enhances etching by thermahzed neutral active species. In microelectronic materials etching, investigators have systematically studied etching product yield and product kinetic energy as a function of ion mass, ion energy and angle of incidence; data on temperature dependence of etching are more limited. By contrast, the temperature dependence of etching C and C-composites in fusion technology has been studied extensively, but there is a lack of data on ion mass and angle dependence, and on the kinetic energy of products. There appears to be no comparable data on ion-assisted etching of materials in typical space en~ronments. These fundamental parameters are essential for formulating and testing models of ion-enhanced etching chemistry. The available data are discussed in terms of phenomenological models and calculations that have been developed. It is clear that further work will be required to provide a solid understanding of the phenomena discussed in this review.

Elsevier eBooks, 1989

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