ALBERT

Notes: The effects of argon-ion sputtering and atmospheric exposure on the composition and structure of plasma-deposited (PD) silicon nitride films were studied using x-ray photoelectron spectroscopy. PD silicon nitride samples were transferred directly from the plasma deposition chamber into the analysis chamber without ambient exposure. Samples exposed to ambient oxidized, with an oxidation rate that depended upon deposition temperature. Ion energies of 500–4000 eV were used to sputter sample surfaces. Preferential sputtering was observed at all energies, with the lower energies creating less compositional and structural modification. Films deposited at lower temperatures exhibited pronounced preferential sputtering of nitrogen, particularly NHx species. Ion milling was found to be unacceptable as a means of surface cleaning PD silicon nitride since even qualitative N:Si composition trends were modified by sputtering.

Notes: The effect of deposition conditions on the structure and composition of plasma deposited silicon nitride films was studied using x-ray photoelectron spectroscopy. Plasma deposited silicon nitride films were transferred directly from the deposition chamber into a surface analysis system, thereby permitting analysis of as-deposited films without modification due to ion sputtering. Plasma deposited silicon nitride films with N:Si ratios from 1.8–0.3 were deposited using SiH4, NH3, N2, and H2 as the source gases. The N:Si ratio in the films increased with increasing nitrogen concentration in the gas phase. Changes in the deposition power or the substrate temperature also influenced the N:Si ratio. Large differences in the film structure were observed for plasma deposited silicon nitride films formed with NH3 compared to N2 with respect to deposition temperature variations.

Notes: Ion and neutral species were sampled from a H2/WF6 tungsten deposition atmosphere (with and without plasma enhancement) by a line-of-sight quadrupole mass spectrometer and cylindrical mirror ion energy analyzer. These diagnostics were used to investigate the influence of neutral and ion flux on the resistivity and morphology of α- and β-tungsten films. In all depositions, WF, WF2, and WF6 were the principle tungsten-fluorine species while WF+5 was the primary plasma-generated ion. Variation of α-tungsten film properties with thickness was dominated by impurities and defects incorporated early in the deposition and by domain size. Plasma-enhanced chemical vapor-deposited films exhibited lower resistivity, and higher temperature coefficient of resistivity and domain size compared to low-pressure chemical vapor deposition films. The variation of α-tungsten properties with increasing ion-bombardment energies was consistent with enhanced sputtering and damage production. Low-resistivity small-domain films were deposited at low frequencies while low-energy high-current bombardment conditions were conducive to domain growth. Nucleation and growth of β tungsten required oxygen rather than fluorine impurities.

Notes: The technique of in situ Fourier transform infrared (FTIR) absorption spectroscopy has been used to determine rotational temperatures and the extent of dissociation of N2 O in a radio-frequency (rf) glow discharge. Measurements were made at 0.65 cm−1 resolution on 13.56-MHz plasmas at 500 mTorr, with an input flowrate of 40 sccm, and powers of 10 and 30 W. Temperature and dissociation information estimates are based upon analysis of P branch rotational lines of the 2ν1 harmonic and ν1 +ν3 combination band of the molecule. Line intensities are corrected for instrument-induced distortion. Under the conditions investigated, rotational temperatures are between 335 and 420 K, and dissociation ranges from 45% to 75%. Both rotational temperature and dissociation increase with rf power.

Notes: Bromine atom concentrations in Br2 discharges were measured by Br2 absorption spectroscopy. At 3.7 MHz, the dissociation of Br2 increased with power, reaching a maximum of ∼40%. The aluminum etch rate was proportional to the bromine atom concentration. In the discharge, atoms etched aluminum 20 times faster than molecules. The etch product molecule appears to be reversibly physisorbed on the brominated surface with an apparent binding energy of ∼0.2 eV/molecule.

Notes: A single-element rotating-polarizer ellipsometer (psi-meter) was used for in situ characterization of the thermodynamic and kinetic behavior of poly-(methyl methacrylate), PMMA, thin films (1.2 μm) in solvent/nonsolvent binary mixtures of methyl ethyl ketone/isopropanol (MEK/IPA) and methyl isobutyl ketone/methanol (MIBK/MeOH). Thermodynamic effects were inferred from equilibrium behavior by the degree of swelling and polymer-solvent solubility. A sharp transition between complete solubility and almost total insolubility was observed in a narrow concentration range near 50:50 (by volume) solvent/nonsolvent for both MEK/IPA and MIBK/MeOH. In the insoluble regime, the polymer was found to swell up to three times the initial thickness. At 50:50 MEK/IPA, a temperature decrease from 24.8 to 18.4 °C caused a change from complete dissolution to combined swelling/dissolution behavior and rendered the PMMA film only 68% soluble. Kinetic effects were determined by dissolution and penetration rate measurements. A constant penetration velocity was observed for almost all compositions for both binary solvent mixtures with Case II transport assumptions providing good agreement with experimental results. For MEK/IPA, penetration rates increased with increasing MEK concentration. For MIBK/MeOH, however, a maximum was observed at 60:40 MIBK/MeOH.

Notes: An electron cyclotron resonance plasma processing system was used to etch hardbaked KTI-820 photoresist from single crystal silicon wafers, silicon dioxide films and patterned multilayer structures. Etch rates of 1500 nm/minute were observed at a substrate temperature below 373 K in a Pforward=750 W, 0.13-Pa ECR oxygen plasma with no applied substrate bias. The etch rate increased linearly with increasing power from Pforward=300–750 W. Etch rate was a complicated function of pressure and residence time, but a modified adsorption-reaction-ion-stimulated desorption rate expression could be used to fit the data. Etch rates decreased for increasing oxygen residence time at low operating pressures due to a combination of polymeric film formation of reaction products and reactant (atomic oxygen) depletion. Maximum etch rates were observed at approximately 0.13 Pa for all residence times. Multilayer photoresist structures were etched at various pressures as well as at a 45° angle to the incident plasma stream. Etch profiles for the variable angle runs indicated that the etch rate was strongly dependent on ion flux. Etch anisotropy increased with decreasing pressure, consistent with increased ion bombardment energy. The degree of anisotropy was, however, limited due to a non-normal component of ion energy, which has been interpreted previously as an ion temperature.

Notes: Aging of proportional counters in CF4/iC4H10 mixtures is studied as a function of gas composition. Anode surfaces are analyzed by Auger electron spectroscopy. Anode-wire deposits are formed from 95/5 and 90/10 mixtures of CF4/iC4H10; etching of deposits occurs in 50/50 and 80/20 mixtures of CF4/iC4H10 and in pure CF4. Gold-plated wires are resistant to aging resulting from chemical attack by CF4, but non-gold-plated wires are too reactive for use in CF4-containing gases. An apparent cathode aging process resulting in loss of gain rather than in a self-sustained discharge current is observed in CF4 and CF4-rich gases. Principles of low-pressure rf plasma chemistry are used to interpret the plasma chemistry in avalanches (≥1 atm, dc). To understand anode aging in CF4/iC4H10 gases, a four-part model is developed considering: (i) plasma polymerization of iC4H10; (ii) etching of wire deposits by CF4; (iii) deposition that occurs as a result of radical scavenging in strongly etching environments; and (iv) reactivity of the wire surface. Practical guidelines suggested by the model and application of the model to other fluorine-containing gases are discussed.

Notes: Thin (3–300-nm) oxides were grown on single-crystal silicon substrates at temperatures from 523 to 673 K in a low-pressure electron cyclotron resonance (ECR) oxygen plasma. Oxides were grown under floating, anodic or cathodic bias conditions, although only the oxides grown under floating or anodic bias conditions are acceptable for use as gate dielectrics in metal-oxide-semiconductor technology. Oxide thickness uniformity as measured by ellipsometry decreased with increasing oxidation time for all bias conditions. Oxidation kinetics under anodic conditions can be explained by negatively charged atomic oxygen, O−, transport limited growth. Constant current anodizations yielded three regions of growth: (1) a concentration gradient dominated regime for oxides thinner than 10 nm, (2) a field dominated regime with ohmic charged oxidant transport for oxide thickness in the range of 10 nm to approximately 100 nm, and (3) a space-charge limited regime for films thicker than approximately 100 nm. The relationship between oxide thickness (xox), overall potential drop (Vox) and ion current (ji) in the space-charge limited transport region was of the form: ji ∝ V2ox/x3ox. Transmission electron microscopy analysis of 5–60-nm-thick anodized films indicated that the silicon-silicon dioxide interface was indistinguishable from that of thermal oxides grown at 1123 K.High-frequency capacitance-voltage (C-V) and ramped bias current-voltage (I-V) studies performed on 5.4–30-nm gate thickness capacitors indicated that the as-grown ECR films had high levels of fixed oxide charge ((approximately-greater-than)1011 cm−2) and interface traps ((approximately-greater-than)1012 cm−2 eV−1). The fixed charge level could be reduced to ≈4×1010 cm−2 by a 20 min polysilicon gate activation anneal at 1123 K in nitrogen; the interface trap density at mid-band gap decreased to ≈(1–2)×1011 cm−2 eV−1 after this process. The mean breakdown strength for anodic oxides grown under optimum conditions was 10.87±0.83 MV cm−1. Electrical properties of the 5.4–8-nm gates compared well with thicker films and control dry thermal oxides of similar thicknesses.