In this work, a novel chlorodisilane precursor, pentachlorodisilane (PCDS, HSiCl), was investigated for the growth of silicon nitride (SiN ) via hollow cathode plasma-enhanced atomic layer deposition (PEALD). A well-defined self-limiting growth behavior was successfully demonstrated over the growth temperature range of 270-360 °C. At identical process conditions, PCDS not only demonstrated approximately>20% higher growth per cycle than that of a commercially available chlorodisilane precursor, hexachlorodisilane (SiCl), but also delivered a better or at least comparable film quality determined by characterizing the refractive index, wet etch rate, and density of the films. The composition of the SiN films grown at 360 °C using PCDS, as determined by X-ray photoelectron spectroscopy, showed low O content (∼2 at. %) and Cl content (<1 at. %; below the detection limit). Fourier transform infrared spectroscopy spectra suggested that N-H bonds were the dominant hydrogen-containing bonds in the SiN films without a significant amount of Si-H bonds originating from the precursor molecules. The possible surface reaction pathways of the PEALD SiN using PCDS on the surface terminated with amine groups (-NH and -NH-) are proposed. The PEALD SiN films grown using PCDS also exhibited a leakage current density as low as 1-2 nA/cm at 2 MV/cm and a breakdown electric field as high as ∼12 MV/cm.

In this work, effects of NH3/N2 and N2-H2/Ar plasma gases for the growth of PEALD SiNx films using pentachlorodisilane (PCDS, HSi2Cl5) were studied using a hollow cathode PEALD system. At identical process conditions, the combination of PCDS and N2−H2/Ar plasma showed a relatively lower (approximately < 10 %) growth rate as compared to NH3/N2 plasma under a range of process temperatures (240−300 °C) whereas the wet etch resistance to HF acid was improved (> 1.6 nm/min, 500:1 HF). Using XPS and FTIR analysis, it was identified that N2−H2/Ar gas mixture results in a Si-rich SiNx film with less N−Hx bonds when compared to NH3/N2 mixture, thereby resulting in a decreased wet etch rate.

A new alkaloid, ClsH2sOSn, designated flabelline, has been isolated by countercurrent distribution from the extract of Lycopodium$abellifoovme. The structure and stereochemistry of flabelline have been established by its conversion to and preparation from lycopodine.The investigatio~l of the alkaloids of Lycopodiumflebellifo~rne was undertaken by nfanske and 1Iarion in 1942 (1). They reported the isolation of lycopodine, the bases L1 to LG, and nicotine. Base L l has since been shown to be dihydrolycopodine (2), L2 to be acetyldihydrolycopodine (3), and LG to be a mixture of two compounds, a-and P-obscurine (4).T h e structures of lycopodine and its derivatives (2) and the obscurines ( 5 ) are now kllown.Flabelliformi~le, a hydroxy derivative of lycopodine, was recently isolated from this plant, and its structure elucidated (6).In this coinmunication we wish to report the isolation and structural elucidation of flabelline, another ininor alkaloid of L. j?abellzforme. The separation procedure used in working up the alkaloids is given in some detail since some fractions are still being investigated and v,rill be reported up011 in a subsequent paper.The alkaloid was extracted according to the procedure of llanslie and Rlarion ( I ) and the bulk of the lycopodine separated by the method of Barclay and lIacLean (7). The residual alkaloids from a number of extractions collected over a period of several years were conlbined and subjected to a preliminary purification as described in the experimental section. The bases were then subjected, on a large scale, to column chromatography on alumina and divided into three fractions-those eluted with chloroform, those eluted with 27, methanol in chloroform, and a residue eluted wit11 5yo methanol in chloroform. Froin the chloroform fraction, flabelliforinine containing some dihydrolycopodine separated upon treatment with ether. The nlother liquor fro111 the separation of flabelliforrnine was concentrated and the residual bases distributed between chloroform and pH 6.0 citratephosphate buffer in a 12-funnel distribution. The distribution was carried out on a large scale and served merely to separate the weak from the strong b'tses. I\/Iany more transfers with a much smaller amount of base would have been necessary to achieve discrete separation of individual bases.Fractions 1 and 2 from the distribution were allnost pure dihydrolycopodine; fractions 3 and 4, a mixture of dihydrolycopodine and flabelline; and fraction 5, a mixture of

A new structural isomer of nonasilane, 2,2,4,4-tetrasilylpentasilane or (H3Si)3SiSiH2Si­(SiH3)3, is formed in disproportionational condensation of neopentasilane. This reaction can be catalyzed by a freshly cleaned borosilicate surface, and the catalyzed reaction can have over 85% selectivity for this branched nonasilane near 100 °C. A synthetic method has been developed from this catalytic reaction for making 98 wt % 2,2,4,4-tetrasilylpentasilane. The high-purity 2,2,4,4-tetrasilylpentasilane has a workable shelf life in 316 stainless steel containers.

No abstract