Hydrogenated nanocrystalline silicon (nc-Si : H) films intended for efficient nc-Si : H solar cells are usually made at the transition to the nanocrystalline regime using the plasma-enhanced chemical vapor deposition (PECVD) process. This change occurs within a sensitive process window and is affected by various deposition parameters. This paper reports a study of nc-Si : H films' fabrication by utilizing systematic plasma diagnostics. This work presents a novel approach for plasma processing using radio frequency (RF), ultra high frequency (UHF) and RF/UHF hybrid plasmas. Using careful analysis, efforts are made to investigate the radicals and plasma formation by changing the operating source power and silane (SiH 4 ) concentration. The aim of this work is also to investigate the PECVD process and conditions favorable for the synthesis of nc-Si : H film. For the present study, we systematically use the optical emission spectroscopy (OES), normal, and RF-compensated Langmuir probe (LP) and vacuum ultraviolet absorption spectroscopy diagnostics. Measurements reveal that the OES diagnostic is consistent with the LP measurements. Investigation reveals that UHF power in addition to RF enables higher dissociation of H or SiH radicals and the production of higher plasma density. The combined effect of both RF and UHF sources is used as the hybrid plasma source. Measurements also reveal that inbetween SiH 4 flow rates ∼20-30 sccm, there is significant change in the plasma characteristics that denotes the nc-Si : H−a-Si : H transition region. An atomic hydrogen density (n H ) in the range ≈ (8 − 10) × 10 11 cm −3 and plasma density n 0 ≈ (2 − 3) × 10 11 cm −3 with a silane to hydrogen ratio of 1-2% with high crystallinity has been obtained. Along with the discussion on the effect of frequency on plasma chemistry, this explains the RF power coupling and the role of electrons and ions in plasmas with increasing frequency.

Articles you may be interested inEffects of plasma and vacuum-ultraviolet exposure on the mechanical properties of low-k porous organosilicate glass J. Appl. Phys. 116, 044103 (2014); 10.1063/1.4891501Plasma damage effects on low-k porous organosilicate glass Plasma-induced damage to porous SiOCH ͑p-SiOCH͒ films during organic resist film ashing using dual-frequency capacitively coupled O 2 plasmas was investigated using the pallet for plasma evaluation method developed by our group. The damage was characterized by ellipsometry and Fourier-transform infrared spectroscopy. Individual and synergetic damage associated with vacuum ultraviolet ͑VUV͒ and UV radiation, radicals, and ions in the O 2 plasma were clarified. It was found that the damage was caused not only by radicals but also by synergetic reactions of radicals with VUV and UV radiation emitted by the plasmas. It is noteworthy that the damage induced by plasma exposure without ion bombardment was larger than the damage with ion bombardment. These results differed from those obtained using an H 2 / N 2 plasma for resist ashing. Finally, the mechanism of damage to p-SiOCH caused by O 2 and H 2 / N 2 plasma ashing of organic resist films is discussed. These results are very important in understanding the mechanism of plasma-induced damage to p-SiOCH films.

The gas phase fragmentations of perfluoro-propyl-vinyl ether (PPVE, C 5 F 10 O) are studied experimentally. Dominant fragmentations of PPVE are found to be the result of a dissociative ionization reaction, i.e., CF 3 + via direct bond cleavage, and C 2 F 3 O % and C 3 F 7 O % via electron attachment. Regardless of the appearance energy of around 14.5 eV for the dissociative ionization of CF 3

In a dual-frequency-excited parallel plate capacitively coupled plasma employing a heptafluoro-cyclo-pentene (C5HF7) gas with addition of O2 and dilution in Ar gas, highly selective etching of SiO2 at selectivities of 40 against Si3N4 and 57 against polycrystalline Si was realized. Gas phase fluorocarbon species containing H atoms such as C x HF y (x>2) played key roles in the selective deposition of thick hydrofluorocarbon films that covered the Si3N4 and polycrystalline silicon (poly-Si) surfaces and in the selective etching of SiO2 over the photoresist, SiN, and Si.

The wavelength dependence of SiN x :H/Si interface defect generation caused by vacuum ultraviolet (VUV)/UV radiation from plasma etching processes was investigated. VUV radiation (λ< 200 nm) had almost no impact on the generation of defects at the SiN x :H/Si interface, since all the radiation in this wavelength range was absorbed in the upper SiN x :H film. However, UV radiation (200 < λ< 400 nm) was able to reach the underlying SiN x :H/Si interface and damage the interface. Direct UV radiation reaching the SiN x :H/Si interface dissociated the chemical bonds at the interface and generated interface-trapped charges. The estimated total energy of absorbed photons (E total; 200 < λ< 400 nm) at the interface layer seems to be proportional to the interface-trapped charge density (D it) measured by capacitance–voltage measurement. However, the mechanism underlying the relationship between E total and D it is not yet clear. Visible radiation (λ> 400 nm) had no influence on damage generation on the SiN x :H/Si structure, since the visible radiation was transmitted through upper SiN x :H film and underlying interface layer. The results revealed that UV radiation transmitted through the upper dielectrics can cause the electrical characteristics of underlying metal–oxide–semiconductor (MOS) devices to fluctuate.