How to grow large clusters from SixD+y ions in silane or disilane: Water them!

Abstract

Growth of large cationic clusters is observed in real time for subsilane and subdisilane cations in the presence ofsilane/disilane-water mixtures. SiOt3 and Si 2 Dtb are created by electron impact in the trapped ion cell of a Fourier transform mass spectrometer and their sequential clustering reactions with 5% water: 95% siIane/disiIane are monitored for up to 80 s at total pressures of 10-7 _10-5 Torr. Formation of Six OyO/ clusters out to at least 450amu in silane and 650 amu in disilane can be seen on the available experimental time scales. The early portion of the sequence leading to large clusters has been elucidated for silane. Amazingly, of the possible subsiIane cations, only SiD + reacts with silane and water to form increasingly larger cluster sizes. Reactions of the other subsilane cations, SiD o +i_3, do not continue without apparent limit. Initial growth of SiD + proceeds in a highly specific ·fashion involving the fonllation of two critical doorway ions, Si 4 Dl followed by Si 4 D7 0 + . The growth pattern then fans out to include numerous alternating and parallel reactions with both SiD 4 and D 2 0. Several general features of the growth reactions are seen. Reactions with SiD 4 are noticeably slower than reactions with O 2 O. Cluster growth by bimolecular reaction with SiD 4 and D 2 0 occurs by addition ofSiD z and addition of an oxygen atom, respectively, accompanied by elimination of D2 . Loss of additional molecules of D2 sometimes occurs, particularly as clustering proceeds to large sizes. Cluster growth by termolecular attachment of SiD 4 or D 2 0 is also seen. This process results in the formation of Six DyO/ complexes with Si0 4 and D 2 0 that appear to serve as important intermediates which enhance cluster growth rates as the total pressure is increased. Sequential clustering without apparent limit is only observed for subsilane and subdisilane cations with silane and disilane when water is present. On this basis, it is proposed that low levels of water contamination can provide a key ingredient for the chemistry which leads to the formation of the hydrogenated silicon particles found ubiquitously in silane plasmas.

Hazards of dichlorosilane exhaust deposits from the high-temperature oxide process as determined by FT-ICR mass spectrometry

“…3) indicate the formation of the polysiloxanes occurs when trace water is present along with DCS in the exhaust tubing. This has parallels to the reactions seen in the silane/water system [11], [12] but is even more prolific because of the more easily generated HCl product. The corresponding initial neutral gas reaction results mostly in chlorosiloxanol (similar to reaction 1) that will react with DCS to form dichlorodisiloxane (similar to reaction (4), again with preferential loss of HCl).…”

“…Exposure to significant water vapor should consume any DCS by complete hydroxylation, as exemplified by the long time-delayed high-pressure water reaction (8). Similarly, the protonated form of (OD) Si-O-Si(OD) was also proposed to be the possible terminal species in similar silane/water ion reactions [11]. This species cannot have further reactions with water and so should be quite stable upon exposure to air.…”

“…This was supported by theoretical mechanism details provided by Raghavachari [10], who confirmed a low transition barrier for sequential clustering. Further work lead Reents and Mandich to discover that, through a small addition of water, the cluster sizes were greatly increased [11], [12] and possibly responsible for micron-sized particulate formation. Around the same time, an extensive study of chlorosilane ion-molecule reactions by Murthy and Beauchamp [13] was performed and they determined the relative stabilities of the chlorosilyl ions.…”

On the formation process of luminescing centers in spark-processed silicon

“…11 Furthermore, gas-phase nucleation and glow-dischargeinduced polymerization effects are known to occur in discharge systems which operate at high pressures. 12 The randomly oriented Si nanocrystallites observed in sp-Si were therefore ascribed to such a nucleation procedure during condensation.…”

Behavior of negative ions and aggregation process of particle growth in silane plasma

“…Raghavachari [11][12][13][14] and Mandich et al [15][16][17][18] examined the positive ions in detail and clarified the presence of a termination step which is a bottleneck preventing further growth via positive ions. Consequently, Si-Si and Si-H bonding energy of neutral Si n H m species and that of negative ones have been evaluated quantitatively to investigate the polymerization pathways.…”