Peter C. Wood

Influence of reactant gas composition on selected properties of N-doped hydrogenated amorphous carbon films

Abstract We report a study of N-doped hydrogenated amorphous carbon films deposited using the r.f. (13.56 MHz) self-bias method. While maintaining a constant r.f. power density (3.2 W cm−2), total feed-gas flow rate (45 sccm), initial substrate temperature (87 °C), and deposition gas pressure (69 μbar), we examined the effect of changing the nitrogen-to-carbon ratio (0.0–4.8) in the feed gas on the film properties: specifically the resistivity, compressive stress, Knoop microhardness, density, index (η) of refraction and chemical composition of the film. As the N-to-C ratio in the feed gas was increased from 0.0 to 4.8, up to 15.6 at.%N was incorporated in the film. Nitrogen substituted for carbon and hydrogen in the amorphous matrix and the hydrogen content decreased from ~16.6 to 10.0 at.%. Fourier transform IR spectra of the films showed an increasing concentration of nitrogen-containing functional groups (-NH and nitrile) in the film as the nitrogen concentration [N]in the film increased. At [N] between 0 and 2 at.%, no significant change was seen in η, mechanical properties or atom number density ρN but the resistivity decreased fifty- to eighty-fold. At [N] > 2 at.%, dramatic reductions were seen in the hardness, stress, ρn, η and resistivity. Over the entire doping range, the resistivity of the films decreased nearly 6000-fold, while the intrinsic stress decreased 56% and hardness was reduced by 52%. The change in resistivity at high [N]appears more correlated with hydrogen loss and enlargement of graphitic microclusters induced by nitrogen ion bombardment during film growth rather than with the N content in the film.

Stress reduction for hard amorphous hydrogenated carbon thin films deposited by the self-bias method

Abstract Hard amorphous hydrogenated carbon (a-C:H) thin films were deposited by the r.f. (13.56 MHz) self-bias method using 2-methyl-propane as the source gas. To achieve stress reduction, we used the periodic plasma deposition technique: repeated cycles of alternating 5 s of deposition (plasma on) with 180 s of cooling (plasma off). Substrate temperature changes during the plasma deposition were monitored by a fluorescent/ optical thermosensor. We investigated the film deposition rate, density, and internal stress as functions of the deposition temperature. We found a linear relationship between the internal stress of a-C:H films and the deposition temperature over the range of 0 to 150 °C. The increase in internal film stress from 0.48 to 1.5 GPa, respectively, over this deposition temperature range is the result of the increase in deposition temperature. Within the range of deposition temperature and r.f. power parameters studied, the deposition temperature appeared to play a more significant role in determining the intrinsic film stress than the r.f. power.

Critical Process Variables for Uv-Ozone Etching of Photoresist

The combination of ultraviolet light (UV) and ozone (O 3 ) has been used to remove organic contamination and strip organic materials, such as, photoresist from silicon and gallium arsenide wafers during processing of electronic devices. In this work we examined the effect of key processing variables such as substrate temperature (150-300°C), O 3 concentration ([03], 4-77 g m −3 ), O3/oxygen flow rate (0.5-3.5 L min −1 ), and UV (185 and 254 nm) irradiation on the etch rate of positive photoresist on silicon wafers. The photoresist etch rate increased up to 28-fold over the substrate temperature range of 150-300°C at constant inlet [O 3 ], flow rate and UV irradiation. At constant substrate temperature and reactant flow rate, the etch rate increased an average of 2-fold with an average 5-fold increase in the inlet [O 3 ]. The etch rate also increased at constant substrate temperature and inlet [O 3 ] with increased reactant flow rate. At 150° and 200°C, UV irradiation enhanced the etch rate of photoresist 2 and 4-fold, respectively, compared to etching experiments where UV irradiation was absent. This suggested that the primary etchant species at these temperatures was atomic oxygen created by photodissociation of O 3 . At 250° and 300°C, UV irradiation during etching did not significantly enhance the etch rate, which suggested that at these higher temperatures, the primary etchant species was atomic oxygen generated from the thermal dissociation of O 3 near the wafer surface.

Effect of temperature on the deposition rate and properties of hydrogenated amorphous carbon films

Abstract Hydrogenated amorphous carbon (a-C:H) films were grown from a hydrocarbon vapor (HCV) by the r.f. (13.56 MHz) self-bias method. The temperature increase of 76.2 mm silicon or quartz wafers during film deposition was maintained over a narrow range (1–20 °C) by clamping the wafers to a temperature-controlled cathode and admitting helium between the back side of the wafer and the cathode. Without wafer clamping and helium back-side cooling, wafer temperatures increased as much as 70–100 °C during deposition, depending on the HCV pressure P and negative d.c. self-bias voltage Vb. Films were deposited over ranges of Vb (from −0.4 to −1.8 kV), P (from 6.7 to 40 μbar) and initial wafer temperature Ti (from −10 to 90 °C). At a given P and Vb (i.e. constant ion energy) the deposition rates of a-C:H increased linearly with decreasing Ti, while the film density, Knoop microhardness HK and compressive stress decreased with decreasing Ti. In general, the values of film density, HK and stress were significantly lower for the temperature-controlled depositions than for films deposited in earlier work without temperature control, but at the same or even lower ion energy. The hydrogen content [H], optical gap ET and surface roughness of the films (measured by scanning force microscopy) increased with decreasing Ti. The effect of lower Ti on the deposition rate and film properties is consistent with a film structure containing a significant fraction of voids. These voids are postulated to form as a result of the lower mobilities of impacting species on the surface of the growing film which prevents densification of the film and retards sputtering or loss of hydrogen.

Stability of IRA-45 solid amine resin as a function of carbon dioxide absorption and steam desorption cycling

The removal of CO2 from the NASA Space Stations cabin atmosphere, which may be undertaken by a solid-amine water (steam)-desorbed system, is presently evaluated with a view to long-term amine resin stability and adsorption/desorption cycling by means of an automated laboratory flow-testing facility. While the CO2-adsorption capacity of the IRA-45 amine resin used gradually decreased over time, the rate of degradation significantly decreased after the first 10 cycles. Attention is given to the presence (and possible need for removal) of trimethylamine in the process air downstream of the resin bed.

A flow-system comparison of the reactivities of calcium superoxide and potassium superoxide with carbon dioxide and water vapor

A single pass flow system was used to test the reactivity of calcium superoxide with respiratory gases and the performance was compared to that of potassium superoxide. The KO2 system is used by coal miners as a self-contained unit in rescue operations. Particular attention was given to the reactivity with carbon dioxide and water vapor at different temperatures and partial pressures of oxygen, carbon dioxide, and water vapor. The calcium superoxide beds were found to absorb CO2 and H2O vapor, releasing O2. The KO2 bed, however, released O2 at twice the rate of CO2 absorption at 37 C. It is concluded that the calcium superoxide material is not a suitable replacement for the KO2 bed, although Ca(O2)2 may be added to the KO2 bed to enhance the CO2 absorption.