High growth rate 4H-SiC epitaxial growth using dichlorosilane in a hot-wall CVD reactor

Thick, high quality 4H-SiC epilayers have been grown in a vertical hot-wall chemical vapor deposition system at a high growth rate on (0001) 80 off-axis substrates. We discuss the use of dichlorosilane as the Si-precursor for 4H-SiC epitaxial growth as it provides the most direct decomposition route into SiCl2, which is the predominant growth species in chlorinated chemistries. A specular surface morphology was attained by limiting the hydrogen etch rate until the system was equilibrated at the desired growth temperature. The RMS roughness of the grown films ranged from 0.5-2.0 nm with very few morphological defects (carrots, triangular defects, etc.) being introduced, while enabling growth rates of 30-100 \mum/hr, 5-15 times higher than most conventional growths. Site-competition epitaxy was observed over a wide range of C/Si ratios, with doping concentrations < 1x1014 cm-3 being recorded. X-ray rocking curves indicated that the epilayers were of high crystallinity, with linewidths as narrow as 7.8 arcsec being observed, while microwave photoconductive decay (\muPCD) measurements indicated that these films had high injection (ambipolar) carrier lifetimes in the range of 2 \mus

Improved sub-threshold slope in short channel vertical MOSFETs using FILOX oxidation

This paper investigates the origins of sub-threshold slope degradation in vertical MOSFETs (v-MOSFETs) due to dry etching of the polysilicon surround gate. Control v-MOSFETs exhibit a degradation of sub-threshold slope as the channel length is reduced from 250 to 100 nm, with 100 nm transistors having a value of 125 mV/dec and a DIBL of 210 mV/V. The effect of the polysilicon gate etch is investigated using a frame-gate architecture in which the polysilicon gate overlaps the side of the pillar, thereby protecting the channel from etch damage. This device shows no degradation of short channel effects when the channel length is scaled and exhibits a near-ideal sub-threshold slope of 76 mV/dec and a DIBL of 33 mV/V at a channel length of 100 nm. Gated diode measurements unambiguously demonstrate that this improved sub-threshold slope is due to the elimination of etch damage at the top and bottom of the pillar created during polysilicon gate etch. An alternative method of eliminating dry etch damage is then investigated by optimizing the Fillet Local Oxidation (FILOX). These devices give a sub-threshold slope of 81 mV/dec and a DIBL of 25 mV/V at a channel length of 100 nm. The improved immunity to dry etch damage is due to the creation of a thick protective oxide at the top and bottom of the pillar during the FILOX proces

Risk factors for retinal breaks during macular hole surgery

Masashi Sakamoto, Izumi Yoshida, Ryuya Hashimoto, Hidetaka Masahara, Takatoshi Maeno Department of Ophthalmology, Toho University Sakura Medical Center, Sakura, Japan Purpose: To identify risk factors for retinal breaks during macular hole (MH) surgery.Patients and methods: This retrospective, observational, comparative study included the medical records of 364 consecutive patients (382 eyes) who underwent vitrectomy for MH at Toho University Sakura Medical Center between January 2012 and May 2017. The patients comprised 135 men and 229 women with mean age 67.6&plusmn;8.0 years. Six eyes with a pre-existing retinal tear treated by laser photocoagulation before MH surgery were excluded. Data on sex, age, presence or absence of lattice degeneration, axial length (measured using an IOL Master&reg;), preoperative refraction, whether or not combined lens extraction/vitrectomy had been performed, whether or not the lens was pseudophakic before vitrectomy, and whether or not a posterior vitreous detachment had been created intraoperatively were collected. The lattice degeneration status was classified as none (0), treated using laser photocoagulation (1), or untreated (2).Results: The only item identified in logistic regression analysis with the backward elimination method to be a significant risk factor for retinal breaks during MH surgery was the presence of lattice degeneration (P&lt;0.001).Conclusion: Ophthalmologists should be aware of the increased risk of retinal breaks during MH surgery in eyes with lattice degeneration. Intraoperative retinal breaks may be less likely to occur in eyes with lattice degeneration treated by photocoagulation preoperatively. Keywords: macular hole, iatrogenic retinal breaks, vitrectomy, lattice degeneratio