A variety of diamondlike carbon (DLC) materials were investigated for their potential applications as low-k dielectrics for the back end of the line (BEOL) interconnect structures in ULSI circuits. Hydrogenated DLC and fluorine containing DLC (FDLC) were studied as a low-k interlevel and intralevel dielectrics (ILD), while silicon containing DLC (SiDLC) was studied as a potential low-k etch stop material between adjacent DLC based ILD layers, which can be patterned by oxygen-based plasma etchingIt was found that the dielectric constant (k) of the DLC films can be varied between >3.3 and 2.7 by changing the deposition conditions. The thermal stability of these DLC films was found to be correlated to the values of the dielectric constant, decreasing with decreasing k. While DLC films having dielectric constants k>3.3 appeared to be stable to anneals of 4 hours at 400 °C in He, a film having a dielectric constant of 2.7 was not, losing more than half of its thickness upon exposure to the same anneal. The stresses in the DLC films were found to decrease with decreasing dielectric constant, from 700 MPa to about 250 MPa. FDLC films characterized by a dielectric constant of about 2.8 were found to have similar thermal stability as DLC films with k >3.3. The thermally stable FDLC films have internal stresses <300 MPa and are thus promising candidates as a low-k ILD.For the range of Si contents examined (0-9% C replacement by Si), SiDLC films with a Si content of around 5% appear to provide an effective etch-stop for oxygen RIE of DLC or FDLC films, while retaining desirable electrical characteristics. These films showed a steady state DLC/SiDLC etch rate ratio of about 17, and a dielectric constant only about 30% higher than the 3.3 of DLC.
We report a new source of femtosecond light pulses which is broadly tunable in the infrared. A singly resonant optical parametric oscillator based on a thin crystal of KTiOPO4 is pumped by intracavity femtosecond pulses at 620 nm from a standard colliding-pulse passively mode-locked dye laser. Oscillation results in stable, continuous outputs of femtosecond pulses at 108 Hz repetition rate and milliwatt average power levels in both signal and idler beams. Here we demonstrate tuning from 820 to 920 nm and 1.90 to 2.54 μm with a single set of mirrors. With multiple sets of mirrors, continuously tunable outputs from ∼0.72 to ∼4.5 μm should be possible, making this a uniquely versatile femtosecond laser source.
A device is presented that sweeps out programmable optical delays of 300 ps (or less) at 30 Hz, with shorter-delay scans possible at much higher rates. It is compact, vibration-free, linear to within 0.02%, and has a position repeatability of 1 part in 105. With this scanner and a PC-based signal-averaging data acquisition system, ultrafast autocorrelation measurements with very high signal/noise are demonstrated in both the fs and ps domains.
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