DIFFUSION OF COBALT 987of the least squares line. This is shown in Fig. 5. The activation energy for diffusion, Q, obtained from the least squares line is Q --28 _ 6 kcal/mole Another point of interest is that the square root relation Vh~ holds for most systems of interest for this model. For gold thicknesses of 3.3 #m and temperature of 50~ (along with the corresponding diffusion coefficient D ----10 -19) the time corresponding to F = 0.6 is of the order of 104 years. If we use smaller thicknesses where the fraction might be appreciable, other transport mechanisms, e.g., porosity, would prevail and the model proposed here would not be applicable.
SummaryWe have considered the diffusion of cobalt out of a gold layer. The theory is discussed first to relate measured quantities to diffusion coefficients. Measurements were taken and the appropriate calculations made to obtain values for the diffusion coefficients at different temperatures. Arrhenius plot extrapolations were then made to obtain rough values for the coefficients at lower temperatures.
ABSTRACTA new, multilayer metallization system has been developed for the purpose of fabricating a planar interconnect structure. This system comprises two levels of metal interconnection, and the first-level metal layer is buried in a low temperature CVD A12Os film pyrolytically deposited by Al(i-CsH70)3 at 420~ The metal chosen for both layers is aluminum, and the insulator is phosphosilicate glass. In the metal processing, a self-aligned photolithographic technique is applied in which positive photoresist AZ-1350 plays an important role in forming the first-level A1 layer and the A1203 film. * Electrochemical Society Active Member.
A new, crosslinking positive resist for deep-uv photolithography has been developed. This resist, a copolymer of glycidyl methacrylate and methyl methacrylate (GCM), degrades on irradiation with light from a D2 lamp and has a sensitivity of 0.25 J/cm2. Three-fourths μm line and space patterns are well resolved. It crosslinks at temperatures above 170°C in an inert atmosphere. This enables strengthening of the resist film by heat treatment after pattern delineation,greatly improving the adhesion and thermal properties of the resist. With these improvements, this resist can successfully be used for etching both SiO2 and phosphosilicate glass in a buffered HF solution. It can also be used for dry etching in CF4 plasma. It is preferable to use noncrosslinked GCM for CF4 plasma etching because the etching rate of noncrosslinked GCM is reduced to about one-third that of crosslinked GCM.
The chemical analysis of trace metallic contamination on a wafer can be achieved by using total reflection X-ray fluorescence (TRXRF) with HF condensation and with poly silicon encapsulation secondary ion mass spectroscopy (PC-SIMS). HF condensation can concentrate almost all atoms, such as Fe, Cr, and Ni, within 10 mm of the center of a wafer, which leads to lower detection limits. Poly silicon encapsulation eliminates the surface problems that tend to occur with normal SIMS, which results in good reproducibility. A combination of both methods is suitable for analyzing lower-level contaminations up to 10' atoms/cm2 level for many elements such as transient metals and lightly elemental metals. The application of the analyses to wet cleaning reveals the contamination removal and adhesion effects for various solutions and cleaning procedures, as well as variation between experimental cleaning batches.
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