Analyses of eleven major elements in five howardite

Shallow trench isolation (STI) requires a high quality oxide with superior fill capability provided by High Density Plasma (HDP) oxide. Unfortunately, the HDP deposition process can create large within die topographies that are difficult to polish directly using conventional silica slurries. As a result, etch back integration schemes have traditionally been incorporated for STI polish. A more revolutionary approach is the use of Fixed Abrasive (FA) CMP [1]. FA CMP allows direct STI polish with good planarization/process stability, eliminating the need for prior etch back. The planarization efficiency is strongly dependent on the shape of the pad composites that hold the CeO2 mineral. Fixed abrasive pads with pyramid and pole shapes are available. In this work, three different fixed abrasive pads supplied by 3M corporation were evaluated for STI CMP polish performance using the Obsidian 8200C web format CMP tool. Basic polish characteristics such as planarity (dependence on sub-pad/pattern density), selectivity to topography, oxide dishing and nitride erosion are presented. The FA pads discussed here have been classified as “slow”, “medium” or “fast” depending on blanket oxide removal rate.The slow rate pad had a very high selectivity to topography and very low dishing of the down area oxide. The removal rate of blanket oxide was less than 100 Å/min. The pad was best suited to the polish of isolation trench structures with small, controlled overfill (> 200 Å) across the wafer. A large process window was demonstrated. The removal rate of the “medium” pad also decreased significantly at the onset of planarization with a blanket oxide removal rate of ca. 200 Å/min. Unlike the slow rate pad, the medium rate pad did not provide a suitable overpolish process window required for a manufacturable STI process. It is believed this pad would be a good choice for BPSG polish. In contrast to the slow and medium rate pads, the blanket oxide removal rate of the fast pad was ca. 2000 Å/min with no self-stopping capability at the onset of planarization. The removal rate was extremely center fast, such that it could not be compensated by adjustment of tool parameters. Use of a modified process developed within the DRAM development alliance (DDA) at East Fishkill (IBM/ Infineon) enabled the fast pad to polish deep STI structures that would otherwise be impossible using the slow or medium rate pads.

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This work describes the use of Single Particle Inductively Coupled Plasma Mass Spectrometry (spICP-MS) to measure ceria particle number concentrations and compare changes in size distributions to silicon dioxide wafer removal rates from different chemical mechanical planarization (CMP) processes. Particle number concentrations were measured for the 21 to 559 nm size range at 1 nm size resolution. Changes in the ceria particle size distribution after CMP included a decrease in large (>130 nm) particles, an increase in small (<40 nm) particles, an increase in the total number of particles, and a decrease in median particle size. The decrease in median size was as high as 7% and influenced by flow rate, pressure and pad type. A novel microreplicated CMP pad was used which requires no pad conditioning to ensure consistent pad surface features, and the effect of different pad types on removal rate and particle size was isolated. A decrease in the median particle size correlated with higher silicon dioxide removal rates (R2 = 0.96) for a series of pad types with unique combinations of chemistry and surface features. This new combination of nano particle metrology and control of pad surface features is an innovative tool set for modeling advanced CMP processes.

New data are used to confirm the positive correlation between Mg and Cr in howardites and eucrites, and the identity of the Mg/Cr ratio in the two meteorite groups is established, provided Chaves is treated as an anomalous howardite. Macibini, usually classed as a eucrite, has higher contents of Mg and Cr than all but the cumulate eucrites; the suggestion is made, on the basis of its polymict character, the wide compositional range of its constituent clasts, and its bulk chemistry, that it should be re‐classified as a howardite. The Mg‐Cr relationship in diogenites is one of almost constant Mg but extremely variable Cr. The “average diogenite” plots fairly close to the trend established for the howardites and eucrites, indicative of the genetic link between these three meteorite classes. The silicate fractions of nine mesosiderites studied do not show a close coherence of Mg and Cr. With the exception of Patwar, they contain more Cr than howardites and eucrites, and exhibit greater variation of Cr relative to Mg. The general lack of clear inter‐element trends in these silicate fractions suggests that they had a more complex origin and evolution than the silicates of the achondrites. Preliminary results of quantitative computer modeling of major and trace elements in the eucrites indicate that about 32 percent fractional crystallization of a eucritic liquid of the composition of Sioux County yields a residual liquid similar to Nuevo Laredo; the cumulate produced has the approximate composition of the cumulate eucrite Moama. These results are in agreement with the model developed by Consolmagno and Drake (1977), using the rare earth elements, for a corresponding stage in the solidification of an initial eucritic liquid produced by equilibrium partial melting of the source region of the parent body (Stolper, 1977). Plotting of the Ti concentrations of the meteorites studied against their Fe/Fe+Mg ratios supports Stolper's idea that the eucrites and the Mg‐rich achondrites do not lie on the same liquid line of descent, and shows that the mesosiderite silicates do not conform to either trend.