Akinobu Nasu

Solar cell lifetime evaluation of using different Si-based precursor gases, SiH 4 and SiF 4

In amorphous silicon (a-Si), Si atoms are not all bonded to 4 other silicon atomes in an ordered manner. and this leads to the formation of defects such as Si dangling bonds.H2 used in the a-Si:H film deposition process passivate the dangling bonds by forming Si-H bonds, thus reducing the defect density. However H* in thin hydrogeneited a-Si films is very reactive especially under light exposure and can successfully break Si-Si bonds to create Si-H and a Si* dangling bond. In turn this defects can trap the electron-holes pairs leading to the degradation of cell efficiency. This is believed to be one of the main reasons for the so-called Staebler-Wronski (S-W) effect.[1–4] In our current study, we add SiF4 (Tetrafluorosilane) as an additive gas during the amorphous silicon film deposition process using SiH4. SiF4 is used as an additive to incorporate small controlled amounts of [F] in the amorphous film, which may stabilize the free dandling bond and may decrease the Staebler-Wronski effect. The effects on complete cell performance parameters, such as the cell efficiency, filling factor, Jsc, Voc and light-soaking degradation results are also included in this study.

Stabilization of Moisture-Premixed Copper Chemical Vapor Deposition Precursor and Applicability

Hexafluoroacetylacetonato copper(I) trimethylvinylsilane [Cu(hfac)tmvs] is currently the most documented precursor for copper chemical vapor deposition (CVD) for semiconductor applications. It is well known that some amount of moisture in the process chamber enhances the deposition rate. In the present study, we found that a water-premixed precursor could be made stable provided that the water was free from any trace of dissolved oxygen. Further improvement in stabilization was obtained in both cases by adding free tmvs. The practicality of this water-premixed precursor was also demonstrated for Cu deposition. No difference was observed for the deposited films in terms of their resistivity, crystallography, purity, or uniformity between the water-premix condition and separate addition of moisture. Furthermore, the optimum moisture concentration for copper deposition was lower than the solubility limit of water in the precursor, which makes this solution of practical interest. We conclude that the water-premixed Cu(hfac)tmvs is a suitable and sophisticated solution for application in the copper CVD process that reduces the hardware burden on the tool and limits the number of process variables.