| 1. |
- Wang, J. J., et al.
(författare)
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Low damage, highly anisotropic dry etching of SiC
- 1998
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Ingår i: High Temperature Electronics Conference, 1998. HITEC. 1998 Fourth International. ; , s. 10-14
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Konferensbidrag (refereegranskat)abstract
- A parametric study of the etching characteristics of 6H p+ and n+ SiC and thin film SiC0.5N0.5 in Inductively Coupled Plasma NF3/O2 and NF 3/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF3 percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide (ITO) masks display relatively good etch selectivity over SiC (maximum of 70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF3:O2 conditions
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| 2. |
- Wang, J. J., et al.
(författare)
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ICP etching of SiC
- 1998
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 42:12, s. 2283-2288
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Tidskriftsartikel (refereegranskat)abstract
- A number of different plasma chemistries, including NF3/O2, SF6/O2, SF6/Ar, ICl, IBr, Cl2/ Ar, BCl3/Ar and CH4/H2/Ar, have been investigated for dry etching of 6H and 3C-SiC in an inductively coupled plasma tool. Rates above 2000 Å cm-1 are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl2-based etching does not provide high rates, even though the potential etch products (SiCl4 and CCl4) are volatile. Photoresist masks have poor selectivity over SiC in F2-based plasmas under normal conditions, and ITO or Ni is preferred. © 1998 Published by Elsevier Science Ltd. All rights reserved.
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| 3. |
- Wang, J. J., et al.
(författare)
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Inductively coupled plasma etching of bulk 6H-SiC and thin-film SiCN in NF3 chemistries
- 1998
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - 0734-2101 .- 1520-8559. ; 16:4, s. 2204-2209
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Tidskriftsartikel (refereegranskat)abstract
- A parametric study of the etching characteristics of 6H p+ and n+ SiC and thin-film SiC0.5N0.5 in inductively coupled plasma (ICP) NF3/O2 and NF3/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF3 percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide masks display relatively good etch selectivity over SiC (maximum of ∌70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF3:O2 conditions. © 1998 American Vacuum Society.
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| 4. |
- Wang, J. J., et al.
(författare)
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High rate etching of SiC and SiCN in NF3 inductively coupled plasmas
- 1998
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 42:5, s. 743-747
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Tidskriftsartikel (refereegranskat)abstract
- Etch rates of ∌3,500 Å/min for 6H-SiC and ∌7,500 Å/min for SiC0.5N0.5 were obtained in inductively coupled plasmas with NF3-based chemistries. Similar etch rate trends were achieved with both NF3/O2 and NF3/Ar mixtures. The rates were strong functions of plasma composition, ion energy and ion fluxes, and were independent of conductivity type for SiC. Surface root-mean-square (RMS) roughness were 1-2 nm for etched SiC over a wide range of conditions indicating equi-rate removal of the SiFx and CFx etch products, but SiCN surfaces became extremely rough (RMS roughness > 20 nm) for F2-rich plasma conditions. The etched surfaces of SiC were chemically clean and stoichiometric, with small (<0.2 at%) quantities of N2- or F2- containing residues detected. © 1998 Elsevier Science Ltd. All rights reserved.
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| 5. |
- Wang, J. J., et al.
(författare)
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ICP etching of SiC
- 1997
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Ingår i: Materials Research Society Symposium - Proceedings. - Boston, MA, USA. ; , s. 177-183
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Konferensbidrag (refereegranskat)abstract
- A number of different plasma chemistries, including NF3/O2, SF6/O2, SF6/Ar, ICl, IBr, Cl2/Ar, BCl3/Ar and CH4/H2/Ar, have been investigated for dry etching of 6H and 3C-SiC in a Inductively Coupled Plasma tool. Rates above 2,000 angstroms·cm-1 are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl2-based etching does not provide high rates, even though the potential etch products (SiCl4 and CCl4) are volatile. Photoresist masks have poor selectivity over SiC in F2-based plasmas under normal conditions, and ITO or Ni are preferred.
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| 6. |
- Guo, Jingtao, et al.
(författare)
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Chromatin and Single-Cell RNA- Seq Profiling Reveal Dynamic Signaling and Metabolic Transitions during Human Spermatogonial Stem Cell Development
- 2017
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Ingår i: Cell Stem Cell. - : CELL PRESS. - 1934-5909 .- 1875-9777. ; 21:4, s. 533-546
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Tidskriftsartikel (refereegranskat)abstract
- Human adult spermatogonial stem cells (hSSCs) must balance self-renewal and differentiation. To understand how this is achieved, we profiled DNA methylation and open chromatin (ATAC-seq) in SSEA4(+) hSSCs, analyzed bulk and single-cell RNA transcriptomes (RNA-seq) in SSEA4+ hSSCs and differentiating c-KIT+ spermatogonia, and performed validation studies via immunofluorescence. First, DNA hypomethylation at embryonic developmental genes supports their epigenetic "poising'' in hSSCs for future/embryonic expression, while core pluripotency genes (OCT4 and NANOG) were transcriptionally and epigenetically repressed. Interestingly, open chromatin in hSSCs was strikingly enriched in binding sites for pioneer factors (NFYA/B, DMRT1, and hormone receptors). Remarkably, single-cell RNA-seq clustering analysis identified four cellular/developmental states during hSSC differentiation, involving major transitions in cell-cycle and transcriptional regulators, splicing and signaling factors, and glucose/mitochondria regulators. Overall, our results outline the dynamic chromatin/transcription landscape operating in hSSCs and identify crucial molecular pathways that accompany the transition from quiescence to proliferation and differentiation.
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| 7. |
- Guo, Jingtao, et al.
(författare)
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The adult human testis transcriptional cell atlas
- 2018
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Ingår i: Cell Research. - : INST BIOCHEMISTRY & CELL BIOLOGY. - 1001-0602 .- 1748-7838. ; 28, s. 1141-1157
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Tidskriftsartikel (refereegranskat)abstract
- Human adult spermatogenesis balances spermatogonial stem cell (SSC) self-renewal and differentiation, alongside complex germ cell-niche interactions, to ensure long-term fertility and faithful genome propagation. Here, we performed single-cell RNA sequencing of similar to 6500 testicular cells from young adults. We found five niche/somatic cell types (Leydig, myoid, Sertoli, endothelial, macrophage), and observed germline-niche interactions and key human-mouse differences. Spermatogenesis, including meiosis, was reconstructed computationally, revealing sequential coding, non-coding, and repeat-element transcriptional signatures. Interestingly, we identified five discrete transcriptional/developmental spermatogonial states, including a novel early SSC state, termed State 0. Epigenetic features and nascent transcription analyses suggested developmental plasticity within spermatogonial States. To understand the origin of State 0, we profiled testicular cells from infants, and identified distinct similarities between adult State 0 and infant SSCs. Overall, our datasets describe key transcriptional and epigenetic signatures of the normal adult human testis, and provide new insights into germ cell developmental transitions and plasticity.
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| 8. |
- Guo, Jingtao, et al.
(författare)
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The Dynamic Transcriptional Cell Atlas of Testis Development during Human Puberty
- 2020
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Ingår i: Cell Stem Cell. - : CELL PRESS. - 1934-5909 .- 1875-9777. ; 26:2, s. 262-
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Tidskriftsartikel (refereegranskat)abstract
- The human testis undergoes dramatic developmental and structural changes during puberty, including proliferation and maturation of somatic niche cells, and the onset of spermatogenesis. To characterize this understudied process, we profiled and analyzed single-cell transcriptomes of similar to 10,000 testicular cells from four boys spanning puberty and compared them to those of infants and adults. During puberty, undifferentiated spermatogonia sequentially expand and differentiate prior to the initiation of gametogenesis. Notably, we identify a common pre-pubertal progenitor for Leydig and myoid cells and delineate candidate factors controlling pubertal differentiation. Furthermore, pre-pubertal Sertoli cells exhibit two distinct transcriptional states differing in metabolic profiles before converging to an alternative single mature population during puberty. Roles for testosterone in Sertoli cell maturation, antimicrobial peptide secretion, and spermatogonial differentiation are further highlighted through single-cell analysis of testosterone-suppressed transfemale testes. Taken together, our transcriptional atlas of the developing human testis provides multiple insights into developmental changes and key factors accompanying male puberty.
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