bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Ethylene Pathway Mutations upon Expression of the Ethylene Receptor ETR1 from Arabidopsis
Authors: Zhao Xue-Chu , Qu Xiang , Mathews Dennis E. , Schaller G. Eric
Published: December 2002

The ethylene receptor family of Arabidopsis consists of five members, one of these being ETR1. The effect of ethylene pathway mutations upon expression of ETR1 was examined. For this purpose, ETR1 levels were quantified in mutant backgrounds containing receptor loss-of-function mutations, ethylene-insensitive mutations, and constitutive ethylene response mutations. Ethylene-insensitive mutations of ETR1 resulted in a posttranscriptional increase in levels of the mutant receptor. Treatment of seedlings with silver, which leads to ethylene insensitivity, also resulted in an increase in levels of ETR1. Loss-of-function mutations of ETR1 resulted in both transcriptional and posttranscriptional changes in levels of the receptor. Most other ethylene pathway mutations, including a newly isolated T-DNA insertion mutation in the gene encoding the ethylene receptor ERS1, had relatively minor effects upon the expression of ETR1. Our results indicate that mutations in ETR1 can affect expression at the posttranscriptional level, and suggest that these posttranscriptional changes may contribute to the phenotypes observed in the mutants. Our results also refine the model on how mutations in ethylene receptors are able to confer dominant ethylene insensitivity upon plants.
Convergence of Calcium Signaling Pathways of Pathogenic Elicitors and Abscisic Acid in Arabidopsis Guard Cells
Authors: Klüsener Birgit , Young Jared J. , Murata Yoshiyuki , Allen Gethyn J. , Mori Izumi C. , Hugouvieux Veronique , Schroeder Julian I.
Published: December 2002

A variety of stimuli, such as abscisic acid (ABA), reactive oxygen species (ROS), and elicitors of plant defense reactions, have been shown to induce stomatal closure. Our study addresses commonalities in the signaling pathways that these stimuli trigger. A recent report showed that both ABA and ROS stimulate an NADPH-dependent, hyperpolarization-activated Ca2+ influx current in Arabidopsis guard cells termed “ICa” (Z.M. Pei, Y. Murata, G. Benning, S. Thomine, B. Klüsener, G.J. Allen, E. Grill, J.I. Schroeder, Nature [2002] 406: 731–734). We found that yeast (Saccharomyces cerevisiae) elicitor and chitosan, both elicitors of plant defense responses, also activate this current and activation requires cytosolic NAD(P)H. These elicitors also induced elevations in the concentration of free cytosolic calcium ([Ca2+]cyt) and stomatal closure in guard cells. ABA and ROS elicited [Ca2+]cytoscillations in guard cells only when extracellular Ca2+was present. In a 5 mm KCl extracellular buffer, 45% of guard cells exhibited spontaneous [Ca2+]cytoscillations that differed in their kinetic properties from ABA-induced Ca2+ increases. These spontaneous [Ca2+]cyt oscillations also required the availability of extracellular Ca2+ and depended on the extracellular potassium concentration. Interestingly, when ABA was applied to spontaneously oscillating cells, ABA caused cessation of [Ca2+]cyt elevations in 62 of 101 cells, revealing a new mode of ABA signaling. These data show that fungal elicitors activate a shared branch with ABA in the stress signal transduction pathway in guard cells that activates plasma membrane ICa channels and support a requirement for extracellular Ca2+ for elicitor and ABA signaling, as well as for cellular [Ca2+]cyt oscillation maintenance.
Down-Regulation of Caffeic Acid O-Methyltransferase in Maize Revisited Using a Transgenic Approach
Authors: Piquemal Joel , Chamayou Simon , Nadaud Isabelle , Beckert Michel , Barrière Yves , Mila Isabelle , Lapierre Catherine , Rigau Joan , Puigdomenech Pere , Jauneau Alain , Digonnet Catherine , Boudet Alain-Michel , Goffner Deborah , Pichon Magalie
Published: December 2002

Transgenic maize (Zea mays) plants were generated with a construct harboring a maize caffeic acidO-methyltransferase (COMT) cDNA in the antisense (AS) orientation under the control of the maize Adh1(alcohol dehydrogenase) promoter. Adh1-driven β-glucuronidase expression was localized in vascular tissues and lignifying sclerenchyma, indicating its suitability in transgenic experiments aimed at modifying lignin content and composition. One line of AS plants, COMT-AS, displayed a significant reduction in COMT activity (15%–30% residual activity) and barely detectable amounts of COMT protein as determined by western-blot analysis. In this line, transgenes were shown to be stably integrated in the genome and transmitted to the progeny. Biochemical analysis of COMT-AS showed: (a) a strong decrease in Klason lignin content at the flowering stage, (b) a decrease in syringyl units, (c) a lowerp-coumaric acid content, and (d) the occurrence of unusual 5-OH guaiacyl units. These results are reminiscent of some characteristics already observed for the maize bm3(brown-midrib3) mutant, as well as for COMT down-regulated dicots. However, as compared with bm3, COMT down-regulation in the COMT-AS line is less severe in that it is restricted to sclerenchyma cells. To our knowledge, this is the first time that an AS strategy has been applied to modify lignin biosynthesis in a grass species.
The sac Mutants of Chlamydomonas reinhardtii Reveal Transcriptional and Posttranscriptional Control of Cysteine Biosynthesis
Authors: Ravina Cristina G. , Chang Chwenn-In , Tsakraklides George P. , McDermott Jeffery P. , Vega Jose M. , Leustek Thomas , Gotor Cecilia , Davies John P.
Published: December 2002

Algae and vascular plants are cysteine (Cys) prototrophs. They are able to import, reduce, and assimilate sulfate into Cys, methionine, and other organic sulfur-containing compounds. Characterization of genes encoding the enzymes required for Cys biosynthesis from the unicellular green alga Chlamydomonas reinhardtii reveals that transcriptional and posttranscriptional mechanisms regulate the pathway. The derived amino acid sequences of the C.  reinhardtiigenes encoding 5′-adenylylsulfate (APS) reductase and serine (Ser) acetyltransferase are orthologous to sequences from vascular plants. The Cys biosynthetic pathway of C.  reinhardtii is regulated by sulfate availability. The steady-state level of transcripts and activity of ATP sulfurylase, APS reductase, Ser acetyltransferase, and O-acetyl-Ser (thiol) lyase increase when cells are deprived of sulfate. Thesac1 mutation, which impairs C.  reinhardtii ability to acclimate to sulfur-deficient conditions, prevents the increase in accumulation of the transcripts encoding these enzymes and also prevents the increase in activity of all the enzymes except APS reductase. The sac2 mutation, which does not affect accumulation of APS reductase transcripts, blocks the increase in APS reductase activity. These results suggest that APS reductase activity is regulated posttranscriptionally in aSAC2-dependent process.
Tip-Growing Cells of the Moss Ceratodon purpureus Are Gravitropic in High-Density Media
Authors: Schwuchow Jochen Michael , Kern Volker Dieter , Sack Fred David
Published: December 2002

Gravity sensing in plants and algae is hypothesized to rely upon either the mass of the entire cell or that of sedimenting organelles (statoliths). Protonemata of the moss Ceratodon purpureus show upward gravitropism and contain amyloplasts that sediment. If moss sensing were whole-cell based, then media denser than the cell should prevent gravitropism or reverse its direction. Cells that were inverted or reoriented to the horizontal displayed distinct negative gravitropism in solutions of iodixanol with densities of 1.052 to 1.320 as well as in bovine serum albumin solutions with densities of 1.037 to 1.184 g cm−3. Studies using tagged molecules of different sizes and calculations of diffusion times suggest that both types of media penetrate through the apical cell wall. Estimates of the density of the apical cell range from 1.004 to 1.085. Because protonemata grow upward when the cells have a density that is lower than the surrounding medium, gravitropic sensing probably utilizes an intracellular mass in moss protonemata. These data provide additional support for the idea that sedimenting amyloplasts function as statoliths in gravitropism.
Targeted Analysis of Orthologous Phytochrome A Regions of the Sorghum, Maize, and Rice Genomes using Comparative Gene-Island Sequencing
Authors: Morishige Daryl T. , Childs Kevin L. , Moore L. David , Mullet John E.
Published: December 2002

A “gene-island” sequencing strategy has been developed that expedites the targeted acquisition of orthologous gene sequences from related species for comparative genome analysis. A 152-kb bacterial artificial chromosome (BAC) clone from sorghum (Sorghum bicolor) encoding phytochrome A (PHYA) was fully sequenced, revealing 16 open reading frames with a gene density similar to many regions of the rice (Oryza sativa) genome. The sequences of genes in the orthologous region of the maize (Zea mays) and rice genomes were obtained using the gene-island sequencing method. BAC clones containing the orthologous maize and ricePHYA genes were identified, sheared, subcloned, and probed with the sorghum PHYA-containing BAC DNA. Sequence analysis revealed that approximately 75% of the cross-hybridizing subclones contained sequences orthologous to those within the sorghum PHYA BAC and less than 25% contained repetitive and/or BAC vector DNA sequences. The complete sequence of four genes, including up to 1 kb of their promoter regions, was identified in the maize PHYA BAC. Nine orthologous gene sequences were identified in the rice PHYA BAC. Sequence comparison of the orthologous sorghum and maize genes aided in the identification of exons and conserved regulatory sequences flanking each open reading frame. Within genomic regions where micro-colinearity of genes is absolutely conserved, gene-island sequencing is a particularly useful tool for comparative analysis of genomes between related species.
Molecular Characterization of an Arabidopsis Acyl-Coenzyme A Synthetase Localized on Glyoxysomal Membranes
Authors: Hayashi Hiroshi , De Bellis Luigi , Hayashi Yasuko , Nito Kazumasa , Kato Akira , Hayashi Makoto , Hara-Nishimura Ikuko , Nishimura Mikio
Published: December 2002

In higher plants, fat-storing seeds utilize storage lipids as a source of energy during germination. To enter the β-oxidation pathway, fatty acids need to be activated to acyl-coenzyme As (CoAs) by the enzyme acyl-CoA synthetase (ACS; EC 6.2.1.3). Here, we report the characterization of an Arabidopsis cDNA clone encoding for a glyoxysomal acyl-CoA synthetase designatedAtLACS6. The cDNA sequence is 2,106 bp long and it encodes a polypeptide of 701 amino acids with a calculated molecular mass of 76,617 D. Analysis of the amino-terminal sequence indicates that acyl-CoA synthetase is synthesized as a larger precursor containing a cleavable amino-terminal presequence so that the mature polypeptide size is 663 amino acids. The presequence shows high similarity to the typical PTS2 (peroxisomal targeting signal 2). TheAtLACS6 also shows high amino acid identity to prokaryotic and eukaryotic fatty acyl-CoA synthetases. Immunocytochemical and cell fractionation analyses indicated that theAtLACS6 is localized on glyoxysomal membranes.AtLACS6 was overexpressed in insect cells and purified to near homogeneity. The purified enzyme is particularly active on long-chain fatty acids (C16:0). Results from immunoblot analysis revealed that the expression of both AtLACS6 and β-oxidation enzymes coincide with fatty acid degradation. These data suggested that AtLACS6 might play a regulatory role both in fatty acid import into glyoxysomes by making a complex with other factors, e.g. PMP70, and in fatty acid β-oxidation activating the fatty acids.
Characterization of Three Maize Bacterial Artificial Chromosome Libraries toward Anchoring of the Physical Map to the Genetic Map Using High-Density Bacterial Artificial Chromosome Filter Hybridization
Authors: Yim Young-Sun , Davis Georgia L. , Duru Ngozi A. , Musket Theresa A. , Linton Eric W. , Messing Joachim W. , McMullen Michael D. , Soderlund Carol A. , Polacco Mary L. , Gardiner Jack M. , Coe Edward H.
Published: December 2002

Three maize (Zea mays) bacterial artificial chromosome (BAC) libraries were constructed from inbred line B73. High-density filter sets from all three libraries, made using different restriction enzymes (HindIII,EcoRI, and MboI, respectively), were evaluated with a set of complex probes including the185-bp knob repeat, ribosomal DNA, two telomere-associated repeat sequences, four centromere repeats, the mitochondrial genome, a multifragment chloroplast DNA probe, and bacteriophage λ. The results indicate that the libraries are of high quality with low contamination by organellar and λ-sequences. The use of libraries from multiple enzymes increased the chance of recovering each region of the genome. Ninety maize restriction fragment-length polymorphism core markers were hybridized to filters of the HindIII library, representing 6× coverage of the genome, to initiate development of a framework for anchoring BAC contigs to the intermated B73 × Mo17 genetic map and to mark the bin boundaries on the physical map. All of the clones used as hybridization probes detected at least three BACs. Twenty-two single-copy number core markers identified an average of 7.4 ± 3.3 positive clones, consistent with the expectation of six clones. This information is integrated into fingerprinting data generated by the Arizona Genomics Institute to assemble the BAC contigs using fingerprint contig and contributed to the process of physical map construction.
Comparative Sequence Analysis of the Sorghum RphRegion and the Maize Rp1 Resistance Gene Complex
Authors: Ramakrishna Wusirika , Emberton John , SanMiguel Phillip , Ogden Matthew , Llaca Victor , Messing Joachim , Bennetzen Jeffrey L.
Published: December 2002

A 268-kb chromosomal segment containing sorghum (Sorghum bicolor) genes that are orthologous to the maize (Zea mays) Rp1 disease resistance (R) gene complex was sequenced. A region of approximately 27 kb in sorghum was found to contain five Rp1 homologs, but most have structures indicating that they are not functional. In contrast, maize inbred B73 has 15 Rp1 homologs in two nearby clusters of 250 and 300 kb. As at maize Rp1, the cluster of R gene homologs is interrupted by the presence of several genes that appear to have no resistance role, but these genes were different from the ones found within the maize Rp1complex. More than 200 kb of DNA downstream from the sorghumRp1-orthologous R gene cluster was sequenced and found to contain many duplicated and/or truncated genes. None of the duplications currently exist as simple tandem events, suggesting that numerous rearrangements were required to generate the current genomic structure. Four truncated genes were observed, including one gene that appears to have both 5′ and 3′ deletions. The maize Rp1region is also unusually enriched in truncated genes. Hence, the orthologous maize and sorghum regions share numerous structural features, but all involve events that occurred independently in each species. The data suggest that complex R gene clusters are unusually prone to frequent internal and adjacent chromosomal rearrangements of several types.
Gramene, a Tool for Grass Genomics
Authors: Ware Doreen H. , Jaiswal Pankaj , Ni Junjian , Yap Immanuel V. , Pan Xioakang , Clark Ken Y. , Teytelman Leonid , Schmidt Steven C. , Zhao Wei , Chang Kuan , Cartinhour Sam , Stein Lincoln D. , McCouch Susan R.
Published: December 2002

Gramene (http://www.gramene.org) is a comparative genome mapping database for grasses and a community resource for rice (Oryza sativa). It combines a semi-automatically generated database of cereal genomic and expressed sequence tag sequences, genetic maps, map relations, and publications, with a curated database of rice mutants (genes and alleles), molecular markers, and proteins. Gramene curators read and extract detailed information from published sources, summarize that information in a structured format, and establish links to related objects both inside and outside the database, providing seamless connections between independent sources of information. Genetic, physical, and sequence-based maps of rice serve as the fundamental organizing units and provide a common denominator for moving across species and genera within the grass family. Comparative maps of rice, maize (Zea mays), sorghum (Sorghum bicolor), barley (Hordeum vulgare), wheat (Triticum aestivum), and oat (Avena sativa) are anchored by a set of curated correspondences. In addition to sequence-based mappings found in comparative maps and rice genome displays, Gramene makes extensive use of controlled vocabularies to describe specific biological attributes in ways that permit users to query those domains and make comparisons across taxonomic groups. Proteins are annotated for functional significance using gene ontology terms that have been adopted by numerous model species databases. Genetic variants including phenotypes are annotated using plant ontology terms common to all plants and trait ontology terms that are specific to rice. In this paper, we present a brief overview of the search tools available to the plant research community in Gramene.
Genetic Complexity of Cellulose Synthase A Gene Function in Arabidopsis Embryogenesis
Authors: Beeckman Tom , Przemeck Gerhard K.H. , Stamatiou George , Lau Rachel , Terryn Nancy , De Rycke Riet , Inzé Dirk , Berleth Thomas
Published: December 2002

The products of the cellulose synthase A (CESA) gene family are thought to function as isoforms of the cellulose synthase catalytic subunit, but for most CESA genes, the exact role in plant growth is still unknown. Assessing the function of individual CESA genes will require the identification of the null-mutant phenotypes and of the gene expression profiles for each gene. Here, we report that only four of 10 CESA genes,CESA1, CESA2, CESA3, andCESA9 are significantly expressed in the Arabidopsis embryo. We further identified two new mutations in the RADIALLY SWOLLEN1 (RSW1/CESA1) gene of Arabidopsis that obstruct organized growth in both shoot and root and interfere with cell division and cell expansion already in embryogenesis. One mutation is expected to completely abolish the enzymatic activity of RSW1(CESA1) because it eliminated one of three conserved Asp residues, which are considered essential for β-glycosyltransferase activity. In this presumed null mutant, primary cell walls are still being formed, but are thin, highly undulated, and frequently interrupted. From the heart-stage onward, cell elongation in the embryo axis is severely impaired, and cell width is disproportionally increased. In the embryo, CESA1,CESA2, CESA3, and CESA9are expressed in largely overlapping domains and may act cooperatively in higher order complexes. The embryonic phenotype of the presumedrsw1 null mutant indicates that the RSW1(CESA1) product has a critical, nonredundant function, but is nevertheless not strictly required for primary cell wall formation.
Cloning of β-Primeverosidase from Tea Leaves, a Key Enzyme in Tea Aroma Formation
Authors: Mizutani Masaharu , Nakanishi Hidemitsu , Ema Jun-ichi , Ma Seung-Jin , Noguchi Etsuko , Inohara-Ochiai Misa , Fukuchi-Mizutani Masako , Nakao Masahiro , Sakata Kanzo
Published: December 2002

A β-primeverosidase from tea (Camellia sinensis) plants is a unique disaccharide-specific glycosidase, which hydrolyzes aroma precursors of β-primeverosides (6-O-β-d-xylopyranosyl-β-d-glucopyranosides) to liberate various aroma compounds, and the enzyme is deeply concerned with the floral aroma formation in oolong tea and black tea during the manufacturing process. The β-primeverosidase was purified from fresh leaves of a cultivar for green tea (C. sinensis varsinensis cv Yabukita), and its partial amino acid sequences were determined. The β-primeverosidase cDNA has been isolated from a cDNA library of cv Yabukita using degenerate oligonucleotide primers. The cDNA insert encodes a polypeptide consisting of an N-terminal signal peptide of 28 amino acid residues and a 479-amino acid mature protein. The β-primeverosidase protein sequence was 50% to 60% identical to β-glucosidases from various plants and was classified in a family 1 glycosyl hydrolase. The mature form of the β-primeverosidase expressed in Escherichia coli was able to hydrolyze β-primeverosides to liberate a primeverose unit and aglycons, but did not act on 2-phenylethyl β-d-glucopyranoside. These results indicate that the β-primeverosidase selectively recognizes the β-primeverosides as substrates and specifically hydrolyzes the β-glycosidic bond between the disaccharide and the aglycons. The stereochemistry for enzymatic hydrolysis of 2-phenylethyl β-primeveroside by the β-primeverosidase was followed by 1H-nuclear magnetic resonance spectroscopy, revealing that the enzyme hydrolyzes the β-primeveroside by a retaining mechanism. The roles of the β-primeverosidase in the defense mechanism in tea plants and the floral aroma formation during tea manufacturing process are also discussed.
Silicon oxide contact hole etching employing an environmentally benign process
Authors: Fujita Kazushi , Hori Masaru , Goto Toshio , Ito Masafumi
Published: December 2002

An environmentally benign etching process using a solid material evaporation technique has been investigated for preventing global warming. In this process, a polytetrafluoroethylene is evaporated by a CO2 laser, resulting in production of fluorocarbon species working as the etching species. Therefore, this system employs no perfluorocompound feed gases, which cause global warming, and enables us to design a new plasma chemistry using the solid material. The system was successfully applied to a SiO2 contact hole etching process employing a planar electron cyclotron resonance plasma. The etched profile was successfully controlled by varying the Ar dilution ratio and the process pressure. In a 0.6 μm contact hole and a 0.08 μm trench fabrication process, this novel process enables us to realize high etching performances, where the etching rate of SiO2, selectivities of SiO2/resist, and SiO2/Si were 340 nm/min, 6.8 and 31, respectively, in optimal condition. To clarify the plasma chemistry using solid material evaporation, CFx (x=1–3) radical densities and F atom density were measured by infrared diode laser absorption spectroscopy and actinometric optical emission spectroscopy, and fluorocarbon films deposited on SiO2 were analyzed by x-ray photoelectron spectroscopy. On the basis of these results, the etching mechanism was discussed.
Comparison of atomic force microscopy imaging methods and roughness determinations for a highly polished quartz surface
Authors: Dokou Eleni , Zhang Lanping , Barteau Mark A.
Published: December 2002

The morphology and microstructure of a polished quartz surface have been studied using atomic force microscopy (AFM) under ambient conditions, high vacuum and ultrahigh vacuum. The general features observed in air and vacuum environments are consistent, showing the existence of long corrugations, scratches, and holes. The root-mean-square surface roughness ranged from 0.2 to 0.4 nm. Imaging of hydrophilic surfaces, such as quartz, with contact-mode AFM can be problematic because of the presence of adsorbed water and contamination layers on the surface. Using tapping-mode AFM in air and noncontact mode AFM under vacuum, we are able to study the true structure of the surface; detection of more local features with higher resolution was achieved under ultrahigh-vacuum conditions.
Exploiting intermolecular interactions and self-assembly for ultrahigh resolution nanolithography
Authors: Anderson M. E. , Smith R. K. , Donhauser Z. J. , Hatzor A. , Lewis P. A. , Tan L. P. , Tanaka H. , Horn M. W. , Weiss P. S.
Published: December 2002

The combination of self-, directed, and positional assembly techniques, i.e., “bottom up” fabrication, will be essential for patterning and connecting future nanodevices. Systematic exploration of local intermolecular interactions on surfaces will permit their exploitation for the rational design of molecular-scale surface structures. We use the scanning tunneling microscope to probe the local behavior of self-assembled films at the nanometer scale. The ability to control the molecular placement within and by self-assembled monolayers is a means of patterning surfaces. A monolayer with customized features can be produced by manipulating the dynamics of film formation, which are heavily affected by the selectable intermolecular interactions of adsorbates and the structural components naturally occurring within the films. Additionally, the controlled placement and thickness of self-assembled multilayers created from alternating strata of α,ω-mercaptoalkanoic acids and coordinated metal ions can be developed to form precise “molecular ruler” resists and to assist in the formation of tailored, lithographically defined metal contacts.
121.6 nm radiation source for advanced lithography
Authors: Yan Jianxun , El-Dakrouri Ashraf , Laroussi Mounir , Gupta Mool C.
Published: December 2002

A vacuum ultraviolet (VUV) light source based on a high-pressure cylindrical dielectric barrier discharge (DBD) has been developed. Intense and spectrally clean Lyman-α line at 121.6 nm was obtained by operating a DBD discharge in neon with a small admixture of hydrogen. The spectrum, optical power, stability, and efficiency of the source were measured. The influence of the gas mixture and total gas pressure on the VUV intensity has been investigated. Maximum optical power of 3.2 W and spectral width <0.03 nm was achieved. Power stability of ±2% for 100 h of operation has also been obtained. The newly developed Lyman-α line source at 121.6 nm appears very promising for advanced lithography and other applications.
Evolution of electron projection optics from variable axis immersion lenses to projection reduction exposure with variable axis immersion lenses
Authors: Stickel W. , Pfeiffer H. C. , Golladay S. D. , Gordon M. S.
Published: December 2002

The optics of the electron projection lithography (EPL) system PREVAIL (projection reduction exposure with variable axis immersion lenses) is retraced from its conceptual and practical foundation in IBM’s shaped beam probe-forming tools via the EPL proof-of-concept system to the implementation of the complex three-dimensional curvilinear variable axis lens optics in the Alpha column, part of the first-of-a-kind electron-beam stepper presently under construction by the IBM alliance partner Nikon Corporation. The significant elements of the optics are described, as well as the innovations, which were required to establish an advanced lithography tool viable in an integrated circuit production environment.
High precision stress measurement of ion projection lithography mask membranes
Authors: Torres José L. , Wolfe J. C. , Ruchhoeft Paul , Kennedy Timothy F. , Podolski Joseph , Kragler Karl , Ehrmann Albrecht , Kaesmaier R. , Löschner H.
Published: December 2002

In this article, we describe an instrument for measuring the mean stress of large-area membranes for ion projection lithography (IPL) stencil masks. The apparatus incorporates two improvements over the conventional bulge technique, where the deflection at the center of a membrane is measured as a function of differential pressure across it, that provide a hundred-fold improvement in the precision of the measurement. The first is to simply place the membrane, without an o-ring or mechanical clamp, on an optically flat silicon ring separating the two pressure chambers. This eliminates the in-plane mounting forces that previously resulted in 1–2 MPa errors. The close contact between the integral ring supporting the mask and the silicon ring provides an adequate vacuum seal between the chambers. The second improvement is to provide an isothermal environment to reduce stress errors due to temperature variations in the membrane. As a result, the measured stress is independent of temperature and the standard deviation (1σ̣) of measured stress is 0.02 MPa.
Imprint lithography for curved cross-sectional structure using replicated Ni mold
Authors: Hirai Yoshihiko , Harada Satoshi , Kikuta Hisao , Tanaka Yoshio , Okano Masato , Isaka Satoshi , Kobayasi Michio
Published: December 2002

Fabrication of patterns with curved cross-sectional profiles for diffractive optical elements are demonstrated by imprint lithography using replicated Ni mold. The master mold pattern is fabricated by an electron beam lithography, where dosage distribution is automatically optimized by a computer aided design (CAD) system taking the proximity effects and resist development process into account. Utilizing the CAD system, a modulated pitched resist pattern with polynomial shaped cross-sectional profiles are successfully obtained by poly (methylmethacrylate) (PMMA) on Si substrate. Using the PMMA resist as a master pattern, replicated mold is fabricated by Ni electroforming followed by Ni electroless plating. Fine and curved cross-sectional patterns are successfully transferred to a resist on Si substrate by imprint lithography using the Ni replicated mold. In the same way, fabrication of sine waved and circular curved structures are demonstrated. This method is exceedingly useful for fabrication of integrated diffractive optical elements with a cross-sectional profile.
Improvements in focused ion beam micromachining of interconnect materials
Authors: Gonzalez J. C. , da Silva M. I. N. , Griffis D. P. , Russell P. E.
Published: December 2002

Focused ion beam micromachining (FIBM) of integrated circuits continues to be an important tool for design debug, editing, and verification; for metrology; and for process control. FIBM of copper interconnects has presented challenges not faced when micromachining aluminum interconnects and the introduction of low-k dielectrics present additional challenges. A new approach to chemically assisted FIBM of thin film Cu, SiO2, and SiLK low-k material using polar precursor molecules has been investigated. Polar alcohols were used to reduce the sputter rate of SiO2 and SiLK while having a minimal effect on the Cu sputter rate. A new FIBM process based on the reduction of the FIB Ga+ energy from the typical 25 to 15 keV is also introduced. The new low energy FIBM process was shown to increase the sputter rate of polycrystalline Cu with strong (111) crystallographic texture by a factor of 2.5. This increase in the sputter rate of Cu combined with a slight reduction of the sputter rate of SiO2 and SiLK results in a Cu/SiO2 selectivity of greater than 7 and a Cu/SiLK selectivity of approximately 3. These are the largest selectivity values reported until now for both systems. The Onderdelinden theory of single-crystal sputtering was used to explain this seemingly anomalous increase of the Cu sputter rate with the reduction of the FIB Ga+ energy.
Hydrogen silsesquioxane for direct electron-beam patterning of step and flash imprint lithography templates
Authors: Mancini D. P. , Gehoski K. A. , Ainley E. , Nordquist K. J. , Resnick D. J. , Bailey T. C. , Sreenivasan S. V. , Ekerdt J. G. , Willson C. G.
Published: December 2002

The feasibility of using hydrogen silsesquioxane (HSQ) to directly pattern the relief layer of step and flash imprint lithography (SFIL) templates has been successfully demonstrated. HSQ is a spin-coatable oxide, which is capable of high resolution electron-beam lithography. Negative acting and nonchemically amplified, HSQ has moderate electron-beam sensitivity and excellent processing latitude. In this novel approach, 6 ×6 × 0.25 in.3 quartz photomask substrates are coated with a 60 nm indium tin oxide (ITO) charge dissipation layer and directly electron-beam written using a 100 nm film of HSQ. Direct patterning of an oxide relief layer eliminates the problems of critical dimension control associated with both chromium and oxide etches, both required processes of previous template fabrication schemes. Resolution of isolated and semidense lines of 30 nm has been demonstrated on imprinted wafers using this type of template. During this evaluation, a failure of the release layer to provide a durable nonstick surface on ITO was discovered and investigated. This problem was successfully remedied by depositing a 5 nm oxide layer over the patterned ITO/HSQ template.
Adaptive alignment of photomasks for overlay improvement
Authors: Chen C.-f. , Engelstad R. L. , Lovell E. G. , White D. L. , Wood O. R. , Smith M. K. , Harriott L. R.
Published: December 2002

The International Technology Roadmap for Semiconductors defines a 23 nm overlay error budget at the 65 nm technology node by the year 2007. To meet the stringent requirement, a proof-of-concept adaptive alignment strategy for overlay improvement has been proposed. By positioning a photomask in an adaptive holder that utilizes piezoelectric actuators and passive fixture supports, overlay registration can be significantly improved by deforming the mask with appropriate forces. The desired forces were calculated by solving an inverse problem in which unit loads are applied at actuator sites to determine the mark displacement sensitivities. Tensile loads almost always appeared in the calculated results, indicating a design issue requiring the bonding of corresponding actuators to the mask. Precompressing the mask and superimposing the calculated forces counteracted the tensile loads, but caused degradation of the exact alignment. Design optimization was exploited subsequently to minimize the preload-induced offset residuals at the alignment marks and across the mask. The proposed adaptive alignment procedure is capable of controlling the overlay errors within specified tolerances and can be readily applied to a variety of reticle formats and sizes.
Improved surface treatments for recycled (100) GaAs substrates in view of molecular-beam epitaxy growth: Auger electron spectroscopy, Raman, and secondary ion mass spectrometry analyses
Authors: Négri Fabienne , Bedel-Pereira Eléna
Published: December 2002

The effects of chemical treatments on recycled (100) GaAs surfaces processed in microelectronic industry have been studied. The recycling process consists in establishing reproductive techniques of polishing and chemical cleaning of rejected processed wafers (with diameter of 100 mm) in order to obtain surfaces reusable to molecular-beam epitaxy (MBE). The recycling process is applied to any processed surface whatever the former technological applications and the doping type. Surfaces were first chemically treated in acid and basic solutions (HCl, diluted HF, and NH4OH solutions). Then, thin layers of GaAs by MBE on them have been elaborated to study the chemical quality at the interface. Surfaces and epilayers have been analyzed using Raman and Auger electron spectroscopies (AES) to qualify the crystalline disorder as well as the chemical composition. Also, secondary ion mass spectrometry (SIMS) have been used to determine the level of contamination at the interface epilayer/substrate. A systematic comparison between the various treatments applied on the GaAs substrates has enabled us to obtain a high surface quality suitable for MBE. Specific results of AES and SIMS analyses clearly indicate that the diluted NH4OH solutions remove the carbon contamination and, reduce the polishing residues content and the oxide thickness.
Effect of implant oxide on ultrashallow junction formation
Authors: Lindsay R. , Lauwers A. , Frühauf J. , de Potter M. , Maex K.
Published: December 2002

For optimal device performance in sub-100 nm complementary metal–oxide–semiconductor, the junction is required to have high wafer uniformity, a high peak dopant concentration, a shallow junction depth, and an abrupt profile. In this article, we will show how all these criteria are strongly influenced by the implant oxide for B, BF2, and As. Due mainly to dopant retention, a thicker implant oxide is shown to significantly reduce the peak concentration of spike annealed B junctions causing a degradation in the sheet resistance for a given junction depth. This Rs to Xj tradeoff is further worsened by a soak anneal or annealing in 5% O2 where more dopants outdiffuse from the silicon. This outdiffusion not only lowers the peak concentration, but also degrades the junction abruptness. Both the oxide and the O2 in the ambient also degrade wafer uniformity. Arsenic implanted into the oxide is driven into the junction during annealing and thus the oxide has a lesser effect on peak concentration, abruptness, and uniformity.
Reflection high-energy electron diffraction observation of the dynamics of semiconductor quantum dot formation and decay
Authors: Finnie P. , Riel B. J. , Wasilewski Z. R.
Published: December 2002

The fabrication of nanostructures can be greatly assisted by the use of in situ tools. Reflection high-energy electron diffraction (RHEED) is a classic tool for in situ monitoring of growth by molecular-beam epitaxy, and it has gained renewed relevance for the production of quantum dots. The evolution of RHEED spot intensities provides information about quantum dot ensembles during nucleation, growth, growth interruptions, decay, and dissolution. The integrated RHEED spot intensity evolves in a characteristic way whether InAs or InxGa1−xAs is grown on GaAs(100), and whether quantum dots are growing or decaying. The application of RHEED to practical issues in the growth of quantum dots is described.
Study of focused ion beam response of GaAs in the nanoscale regime
Authors: Lugstein A. , Basnar B. , Bertagnolli E.
Published: December 2002

Focused ion beam (FIB) technology has been demonstrated to be a powerful tool in microfabrication, primarily for semiconductor related processing. The migration of the critical dimensions of devices toward the nanometer regime necessitates the knowledge of fundamental milling process mechanisms to gain full use of the opportunities offered by the focused ion beam technique. We have investigated the influence of declining feature sizes on the focused ion beam response of GaAs. Based on our experimental results, a sputter yield promoting the self-focusing effect combined with a sputter rate increase at oblique angles, an opposing dose deficiency effect, and material redeposition for milling aspect ratios >1 are identified to be responsible for the complex sputter response of GaAs. In addition, the observed preferential etching of arsenic results in local precipitates of mobile Ga-rich residues influencing the fundamental characteristics of FIB patterning, like sputter yield, crater bottom flatness, and ripple formation.
Leveling effects of copper electrolytes with hybrid-mode additives
Authors: Lin Kun-Cheng , Shieh Jia-Min , Chang Shih-Chieh , Dai Bau-Tong , Chen Chia-Fu , Feng Ming-Shiann , Li Ying-Hao
Published: December 2002

100 nm vias were completely filled with copper for interconnect applications using an electrolyte in the presence of polyethylene glycols (PEG) and a hybrid-mode additive, benzotriazole (BTA). Electrochemical analyses indicated that BTA with a higher concentration inhibited the copper deposition rate, whereas BTA with a lower concentration accelerated the copper deposition rate. This electrolyte thus generated an enhanced deposition gradient within a gap because the PEG molecules and the high concentration of BTA, adsorbed at the opening of the gap, inhibited the deposition. Meanwhile, a little BTA diffused into the inner part of the gap and thus accelerated the deposition of copper. Therefore, this two-component (PEG and BTA) additive electrolyte had the capacity of a three-additive bath (accelerators, suppressors, and levelers).
Influence of the surface Si/buried oxide interface on extended defect evolution in silicon-on-insulator scaled to 300 Å
Authors: Saavedra A. F. , Frazer J. , Jones K. S. , Avci I. , Earles S. K. , Law M. E. , Jones E. C.
Published: December 2002

As device dimensions continue to be scaled, incorporation of silicon-on-insulator (SOI) as mainstream complementary metal–oxide–semiconductor technology also increases. This experiment set out to further investigate the effect of the surface Si/buried oxide (BOX) interface on the formation and dissolution of extended defects in SOI. UNIBOND® wafers were thinned to 300, 700, and 1600 Å. Si+ ion implantation was performed from 5 to 40 keV with a constant, nonamorphizing dose of 2×1014 cm−2. Inert ambient furnace anneals were performed at 750 °C for times of 5 min up to 8 h. Transmission electron microscopy was used to study the evolution of extended defects, as well as to quantify the number of trapped interstitials. It is observed that the surface Si/BOX interface does not enhance the dissolution rate of extended defects unless ⩾15% of the dose is truncated by the BOX. Further, no reduction in the trapped interstitial concentration is seen unless ⩾6% of the dose is truncated. It is concluded that the surface Si/BOX interface does not serve as a significant sink for interstitial recombination, as long as the interstitial profile is mostly confined to the surface Si layer.
Multiple-beam interference lithography with electron beam written gratings
Authors: Solak H. H. , David C. , Gobrecht J. , Wang L. , Cerrina F.
Published: December 2002

Interference lithography with multiple beams provides two-dimensional periodic patterns in a single exposure step. It is possible to obtain various symmetries and shapes such as sparse hole arrays or dots on a hexagonal grid. However, when the number of interfering beams exceeds three, the intensity pattern depends strongly on the relative phases of the beams. In this article we show that this problem can be overcome with a scheme where transmission diffraction gratings written on a single substrate create the interfering beams possessing the required phase relations. The relative phases of the diffracted beams are controlled by the relative positions of the gratings in the substrate plane. We used electron beam lithography with an interferometrically controlled stage to obtain the required precise placement of the gratings. This method enabled us to produce hexagonal and square arrays of holes where we used three and four beam configurations, respectively. Moreover, we created sparse hole arrays that have hexagonal and square symmetries with six and eight beam interference. The experiments were carried out in the extreme ultraviolet region with synchrotron radiation and with laser light in the visible spectrum. The technique requires spatially coherent light but it is achromatic and it is not sensitive to small errors in the alignment of the incoming beam.
Single ion implantation for solid state quantum computer development
Authors: Schenkel T. , Persaud A. , Park S. J. , Meijer J. , Kingsley J. R. , McDonald J. W. , Holder J. P. , Bokor J. , Schneider D. H.
Published: December 2002

Several solid state quantum computer schemes are based on the manipulation of electron and/or nuclear spins of single 31P atoms in a solid matrix. The fabrication of qubit arrays requires the placement of individual atoms with nanometer precision and high efficiency. We describe the status of our development of a low energy, single ion implantation scheme for 31Pq+ ions. High ion charge states enable registration of single ion impacts with unity efficiency through the detection of secondary electrons. Imaging contrast in secondary electron emission allows alignment of the implantation and integration with consecutive lithography steps. Critical issues of process integration and resolution limiting factors are discussed.
Particle-induced distortion in extreme ultraviolet lithography reticles during exposure chucking
Authors: Tejeda R. , Engelstad R. , Lovell E. , Blaedel K.
Published: December 2002

Since the goal of extreme ultraviolet lithography is to produce circuit patterns with critical dimensions less than 65 nm, a key to its success will be to identify and minimize the major sources of image placement (IP) error at the wafer. Two sources of IP error are in-plane distortion (IPD) and out-of-plane deformation (OPD) of the patterned reticle during chucking in the exposure tool. Among the many possible causes of IPD and OPD is particle contamination. Small pieces of debris lodged between the reticle and chuck have the potential to distort the pattern that is transferred to the device wafer. Such distortions may consume an unduly large portion of the error budget allotted to image placement. In order to limit these IP errors, it is first necessary to gain a thorough understanding of the behavior of a particle trapped during the chucking process. This article describes the techniques that were used to study these trapped particles and their potential effects on pattern placement accuracy.
Advanced time-multiplexed plasma etching of high aspect ratio silicon structures
Authors: Blauw M. A. , Craciun G. , Sloof W. G. , French P. J. , van der Drift E.
Published: December 2002

An advanced, time-multiplexed plasma etch process for high aspect ratio structures is presented. Compared to the two pulse Bosch process, the technique consists of a sequence of three pulses. The third pulse is tailored to improved depassivation of the trench bottom prior to each etch pulse. Several depassivation chemistries are explored: O2, CO2, and SO2. In a further extension the bias voltage is also pulsed, with the aim to balance the radical and ion-enhanced components in the passivation of the sidewalls and trench bottom. The process extensions lead to improved mask selectivity and substantial range for profile control from fully anisotropic to strongly negatively tapered. The maximum aspect ratio obtained in the Bosch process could not be improved, because the ion angular distribution probably remains the limiting factor. The role of the ions in passivation and etching has been quantified in separate experiments.
Complementary mask pattern split for 8 in. stencil masks in electron projection lithography
Authors: Yamashita Hiroshi , Takahashi Kimitoshi , Amemiya Isao , Takeuchi Kunio , Masaoka Hideki , Takenaka Hiroshi , Yamabe Masaki
Published: December 2002

We have improved the M-Split complementary mask pattern split program and our electron projection lithography (EPL) data conversion system to achieve a practical data processing time and data volume. The system was designed to rehierarchicalize the data, flattened after the subfield split, by extracting polygons that all have an identical shape as a cell. The M-Split stress check function was improved by using a normalized bending moment as a criterion. A clustered computing system was used to reduce the data processing time. The processing time for a complementary mask pattern split without rehierarchicalizing was reduced to 57 min by using the stress check function and a ten PC cluster system −3–10 times as fast as with commercially available EPL data conversion systems. We successfully fabricated a full-size 8 in. Si stencil mask consisting of 8000 subfields using the data for an actual 70 nm design-rule system on chip device to demonstrate the effectiveness of M-Split. With a higher performance PC cluster system and the rehierarchicalizing, we expect to further reduce the M-Split processing time to 10 min.
Technique for preparation of precise wafer cross sections and applications to electron beam lithography of poly(methylmethacrylate) resist
Authors: Hu Wenchuang , Orlova Tatyana , Bernstein Gary H.
Published: December 2002

We have developed a method of cross-sectioning silicon wafers with high placement precision. It is implemented by using optical lithography and deep plasma high aspect ratio etching of a thin line, which is used as the breaking axis. This technique is then applied to cross-sectional scanning electron microscopy (SEM) studies of sub-50 nm electron beam lithography in (poly)methylmethacrylate resist. We also report the development of a process for protecting the resist during SEM examination.