Μm Si Research Articles

Proximity effect in electron beam patterned x-ray masks

Electron beam exposures of 30 nm Au/5 nm Cr/2.2 μm Si x-ray lithography mask structures were carried out at 25, 50, 75, and 100 keV to study the reduction in the proximity effect at higher beam voltages resulting from the loss of backscattered electrons out the backside of the masks. Surprisingly, the thin Au/Cr plating base was found to be the major source of backscattering over distances <1.0 μm. In addition, the plating base served to limit the decrease in the ratio of the backscattered to forward scattered exposure that resulted from increasing the beam voltage. These results indicate that simply increasing the beam voltage will not completely eliminate the proximity effect due to backscattering that arises during the electron beam patterning of x-ray masks.

Anomalous penetration of Cs, Ba and Tl through thin Si films

Proton backscattering studies of 0.1 mol/L aqueous solutions of CsNO 3, Ba(N0 3) 2 and TlNO 3, at atmospheric pressure, have been made through thin (⪅ 0.8 μm) Si windows. In all three cases, the heavy element (Cs, Ba or Tl) was observed to penetrate the Si window and the maximum concentration was centred about the beam position. This can be understood by assuming that mupores of ≈ 100 Å radius occupy 0.01% of the window area. For thicker windows (⪅ 0.9 μm) the effect does not occur.

Response of cotton cultivars to aluminum in solutions with varying silicon concentrations

Abstract Cotton (Gossypium hirsutum L.) is extremely sensitive to Al toxicity. Increasing Si concentration in solution has been reported to alleviate AI toxicity. In this investigation the effects of varying Si concentrations (700, 1400, and 2800 μM Si) on reactive Al (defined as Al reactive with aluminon during 10‐s reaction time, without acidification and heating) was studied in solutions containing either 50, 100 or 200 μM Al during 50 d of aging. An increase in Si concentration had negligible effects on the reactive Al in solutions with 50 or 100 μM Al. However, in solutions with 200 μM Al the reactive Al decreased by 6 to 15% with an increase in Si concentration from 0 to 2800 μM. The effects of either 700, 1400 or 2800 μM Si on root growth of Coker 208, Coker 315, DPL 90, McNair 235, Stoneville 506 and Tifcot 56 cotton cultivars were investigated in solutions containing either 0, 10, 20 or 40 μM Al with 500 μM Ca at pH 4.5. In solutions containing no Al, addition of 700 μM Si improved root growth by...

Low energy positron channeling in silicon

The recently developed low energy (1–60 keV variable) positron beam facility at the University of Western Ontario has been used to study positron channeling through a 0.26 μm Si(100) crystal. Along the 〈100〉 axis, a strong reduction in the wide-angle (12°–15°) scattering yield was observed even at the lowest energy studied (15 keV). The angular widths were consistent with values predicted by Lindhard's classical theory of channeling. The minimum yields agreed with extrapolations from dechanneling measurements made with high energy protons. Measurements were also made at 50 keV along the 〈210〉 and 〈310〉 axes, as well as the (100), (110), and (210) planes. Again, the results were consistent with the classical theory in the manner described above, although the magnitude of the effect was less than that in the case of 〈100〉 channeling. Only slight evidence of a first order diffraction effect was seen in some of the data obtained; however, a rather large degree of positron-electron multiple scattering was presumably responsible for masking out any detailed observation of diffractive features.

Investigation of Quantum States of Fast Electrons under Planar Channeling in Silicon Crystals

AbstractThe angular distributions of (1.87 to 5.7) MeV electrons channeled in 2 μm Si crystals along (100), (110), and (111) atomic planes are measured. The half‐width of measured angular distributions is defined by a critical Lindhard angle. A relation is obtained connecting those energies of electrons at which their angular distributions are similar for various atomic planes. The effect of a “critical energy” under planar channeling of electrons is found and investigated.

Silicon interactions with manganese and aluminum toxicity in sorghum

Abstract Silicon fertilization has been shown to alleviate Mn and Al toxicities in some plants. Experiments were conducted to assess the role of different Si levels on the alleviation of Mn and Al toxicity symptoms and on dry matter yields of sorghum [Sorghum bicolor (L.) Moench] grown in nutrient solutions with toxic levels of Mn and Al. Silicon concentration as high as 1780 μM had no detrimental effects on dry matter yields. At high Si levels (2670 and 3560 μM), shoot dry matter yields decreased, but root dry matter yields did not. Plants grown with 3600, 5400, and 7200 μM Mn showed marked visual toxicity symptoms in shoots but no effects on roots, even though root dry matter yield decreased more than shoot dry matter yield. The toxicity symptoms and the dry matter yield reductions caused by 3600 and 5400 μM Mn were partially alleviated by 1780 and 3560 μM Si, whereas no Si level overcame the severe effects induced by 7200 μM Mn. Plants grown with high Al (296 μM) had reduced root dry matter yields. Sil...

Static 7 GHz frequency divider IC based on a 2 μm Si bipolar technology

A static 8:1 frequency divider IC operating at up to 7 GHz has been realised using a preproduction silicon bipolar technology with 2 μm lithography. This technology is characterised by a self-aligned double polysilicon emitter-base structure and oxide wall isolation. The high upper frequency limit, not yet achieved with comparable 2 μm technologies, was attained by careful circuit design and optimisation.

Variable kinetics of silicon-limited growth inThalassiosira pseudonana(Bacillariophyceae) in response to changed chemical composition of the growth medium

The diatom Thalassiosira pseudonana Hasle & Heimdal was grown in batch culture in one artificial sea-water medium and one fresh-water medium over a range of orthosilicic acid concentrations. Growth rates and cellular silicon quotas were measured in the exponential growth phase. The half-saturation constant of silicon-limited growth was about 0·04 μm Si(OH)4 in the marine medium and about 8·6 μm Si(OH)4 in the freshwater medium, the maximum growth rate being about 2·75 d-1 in both media. Possible reasons for the difference in affinity for silicon in salt and fresh water include differences in pH, ion composition, and osmotic pressure. The distribution of T. pseudonana in nature is in agreement with the experimental data, but the investigation shows the importance of a systematic evaluation of the influence of water chemistry on silicon utilization especially in fresh-water plankton. The cellular silicon content was greater in fresh water and did not vary with substrate concentration as in the marine medium...

GROWTH RATES AND ULTRASTRUCTURE OF SILICEOUS SETAE OF CHAETOCEROS GRACILIS (BACILLARIOPHYCEAE) 12

ABSTRACT The growth of setae in post‐division Chaeloceros gracilis Schütt was triphasic. Following cell separation there was an initial lag phase of about 30 min after which setae grew linearly at rates ranging from 0.20 to 0.38 μm‐min−1. The growth rate was independent of whether diatoms cultured in medium containing 200 μM Si were transferred for experimentation to media containing 10 or 200 μM Si. When developing setae had attained a length of approximately 2 μm, their growth rate slowed as they entered a clearly defined plateau phase. The amount of silicon per unit length of setae was found to be 0.02 pg Si μm−1, and the deposition rate was estimated as 0.005 Pg Si min−1. Transmission electron microscopy revealed an axial structure resembling a microlubule extending the length of each seta and membrane bound polyphosphate bodies postulated to be the energy source for growth and associated biomineralization processes.

A study contradicting the ‘luxury consumption’ of silicon by the marine prasinophycean alga, Platymonas: Smith-Palmer, T., A.S.W. de Freitas, A.G. McInnes, A. Rogerson, A.W. McCulloch and J. McLachlan, 1985. Biol. Oceanogr., 3(3): 315–326

AbstractNatural waters are often low in silicate ion, hence the possible “luxury consumption” of this ion by algae with no known Si-requirement is of major ecological importance to siliceous organisms. A unicellular marine alga, Platymonas sp., was studied in this context under controlled laboratory conditions. Growth rates in pH-regulated cultures were unaffected by silicate concentrations ranging between 1.0 and 230.0 μM Si. No removal of silicate from the medium was observed when the pH of cultures was maintained below 9.0. Without pH control, cultures of Platymonas reached values of pH greater than 9.5, at which time a rapid and essentially complete removal of silicate from the medium was observed. This was not attributable to biological uptake as intracellular silicon was not detected by electron spectroscopic imaging, although a relatively small amount of silicon was observed in association with the cell theca. The sedimented “cell-pellet” harvested from unbuffered cultures at pH > 9.5 contained a f...

Time-resolved and space-resolved Si lattice-temperature measurements during cw laser annealing of Si on sapphire

We have developed an optical technique for in situ measurement of temporal change and spacial profile of Si lattice temperature during cw laser annealing. This technique utilizes time-dependent optical interference in Si films on insulator. By using a microscope for focusing a laser probe beam to 2.0 μm, time-resolved and space-resolved Si lattice-temperatures were measured below the melting point (1412 °C) on a time scale of 10−4–100 s during cw laser annealing of Si on sapphire.

Nonmetallic localization and interaction in one-dimensional (0.1 μm) Si MOSFETs

We have fabricated Si MOSFETs having parallel arrays of narrow (0.1 μm) conducting channels. We observe a divergent, nonmetallic decrease of conductance below 30 K that is in excellent quantitative agreement with the one-dimensional version of the combined theories for weak localization and interaction effects. We also observe structure in the conductance as a function of gate voltage that we attribute to random variations of the density of states, rather than the regular variations expected for simple one-dimensional quantization.

Seeded recrystallization of thick polysilicon films on oxidized 3-in. wafers

The first successful seeded recrystallization of thick, >10 μm Si films deposited on SiO2 is reported. A method of lateral epitaxial growth over oxide (LEGO) has been developed, in which the thick polycrystalline Si films are completely melted by intense photon flux. The epitaxial recrystallization which follows starts at the seeding regions, spaced as far as 1 mm apart, and results in single crystalline Si-on-insulator with a low density of defects. The process is carried out in a special furnace with samples placed between a bank of tungsten halogen lamps and a water-cooled base, allowing uniform and bow-free crystallization of complete 3-in. wafers in ∼60 s.

Sub-Boundary Formation and Suppression in Silicon films Recrystallized by Scanned Zone Melting

ABSTRACTWe observe that the formation of low angle grain boundaries (sub-boundaries) depends strongly on the thickness of the recrystallized Si film. The average lateral spacing between adjacent sub-boundaries increases from 40 μm for 4000Å films to 500 μm for unseeded Si films 30 μm thick. For seeded 30 μm Si films on 1.6 mm by 1.6 mm buried oxide islands, areas exceeding 1.0 mm by 1.0 mm have been recrystallized which are free of all sub-boundaries, but which contain dislocations in other configurations.

TEMPERATURE EFFECTS ON SILICON LIMITED GROWTH OF THE LAKE MICHIGAN DIATOM STEPHANODISCUS MINUTUS (BACILLARIOPHYCEAE)1

ABSTRACTThe effect of temperature on the silicon limited growth and nutrient kinetics of Stephanodiscus minutus Grun. was examined using batch and semicontinuous culture methods. Short‐term batch culture methods gave maximum growth rates which were essentially constant over the temperature range of 10° to 20°C (μ3= 0.71–0.80 d−1). The half‐saturation constant for growth (Ks) was significantly lowest at 10°C (Ks= 0.31 μM Si; 0.22–0.41), and higher at both 15°C (Ks= 1.03 μM Si; 0.68–1.47) and 20°C (Ks= 0.88 μM Si; 0.60–1.22). Two methods were used to evaluate the semicontinuous experiments. The Droop relationship showed that the minimum cell quota was about 1.50 × 10−7 nmol Si cell−1, but there was much overlap in the results at all three temperatures. The Monod growth relationship for the semicontinuous experiments gave estimates of Ks which were lowest at 15°C (Ks= 0.12 μM Si), and higher at 10°C (Ks= 0.68 μM Si) and 20°C (Ks= 1.24 μM Si), although 95% confidence intervals overlapped. The maximum growth rate estimates for the semicontinuous experiments were similar at 10° and 15°, and higher at 20°C, but the number of points used in making the calculations makes the results less reliable than those from batch cultures. Generally, there were no consistent significant differences in the silicon limited growth of S. minutus over the temperature range studied. Our values of Ks for S. minutus are the lowest recorded for a freshwater diatom, and are consistent with the distribution of this species in nature. Generally, this species becomes abundant in areas with high phosphorus loading and very low silicon levels (low Si:P loading rates). Stephanodiscus species are also fossil indicators of eutrophication in north temperate lakes.

Transient Conductance Measurements During Pulsed Laser Annealing

ABSTRACTMeasurements were made of the conductance of single crystal Au-doped Si and silicon-on-sapphire (SOS) during irradiation with 30 nsec ruby laser pulses. After the decay of the photoconductive response, the sample conductance is determined primarily by the thickness and conductivity of the molten layer. For the single crystal Au-doped Si, the solid-liquid interface velocity during recrystallization was determined from the current transient to be 2.5 m/sec for energy densities between 1.9 and 2.6 J/cm2, in close agreement with numerical simulations based on a thermal model of heat flow. SOS samples showed a strongly reduced photoconductive response, allowing the melt front to be observed also. For complete melting of a 0.4 μm Si layer, the regrowth velocity was 2.4 m/sec.

Determination of the Total X-Ray Dose in the SiO2 Layer of Backside Electron Irradiated ICCD Imagers

The voltage and electron fluence dependent total X-ray dose absorbed in the SiO2 layer of intensified charge coupled devices (ICCDs) operated in the backside electron irradiated mode has been calculated. The calculations were based on spectral intensity distribution and absolute dose measurements at what would be the Si-SiO2 interface of an actual device. It is shown that the fraction of the incident electron energy converted into X-rays that is produced and transmitted through the ~10 μm Si substrate is ~1×10-4 at 10 keV and ~3×10-4 at 20 keV. Approximately 1.5 percent of this total transmitted X-ray energy is absorbed in 100 nm SiO2 and between 85-97 percent of that X-ray energy is in the characteristic Kα line at 1.732 keV. The dose deposited in the SiO2 per electron incident on backside of a 10 μm Si substrate is D=9.7×10-14E(keV)2.2 rad(SiO2)/e-cm-2, and of a 13 μm Si substrate it is D = 3.5×10-14E(keV)2.44 rad(SiO2)/e-cm-2. With overcast starlight illuminance levels (~-10-4 Lux) the rate of dose deposition in the oxide of a typical ICCD operated at 10, 15, and 20 kV is 2.3, 6.3, and 12.7 rad(SiO2)/hr., respectively. At these dose rates, and particularly with reduced operating voltages, megarad hardened CCDs in low light level ICCD-TV camera tubes are expected to have useful operating lifetimes up to a hundred thousand hours.

Optical performance of absorber-reflector combinations for photothermal solar energy conversion

For a number of absorber-reflector combinations the reflectance spectrum as well as the figure of merit a/e has been computed numerically in order to find an optimum set of parameters. Values of a/e in excess of 20 result for an absorber consisting of 0.5 μm Ge on a silver reflector, overlaid by 2.0 μm Si carrying a four-layer antirereflection sequence in which the refractive index varies from 2.79 to 1.43. To maximize the optical acceptance angle the antireflection coatings must vary the refractive index in a graded profile from the value of index of silicon to the one of air.

Channeling analysis of stacking defects in epitaxial Si layers

The channeling effect technique has been applied to investigate dechanneling by stacking defects in heteroepitaxially grown silicon. Ion backscattering was performed on 0.9 μm Si layers grown on sapphire as a function of beam energy (1.1–2.5 MeV He +), projectile ion (He +, D +) and crystal direction (〈100〉, 〈111〉, 〈112〉,〈113〉). Transmission electron muscopy analysis revealed the presence of a high density of stacking faults and twin lamellae. A model based on the new interior surfaces presented by such stacking defects is used to calculate the dechanneling cross section, and the disorder profiles are obtained from the experimental dechanneled fractions in terms of displaced rows per unit volume. Direct backscattering of channeled particles from the defects is neglected since the dechanneling cross section per row is about one order of magnitude larger than that per displaced atom. The resulting defect depth distributions are independent of beam energy and projectile ion, and give improved quantitative agreement with previous studies. The application of channeling to stackingdefect measurements requires a minimum density of ∼10 15 displaced rows/cm 2.

On the barium data from the Atlantic GEOSECS expedition

Barium profiles at the Atlantic stations of the Geochemical Ocean Sections (GEOSECS) Program are remarkably similar to those for silicate and alkalinity. In nutrient depleted surface waters barium ranges between 36 and 44 nm kg −1: the Arctic overflows have values between 44 and 49 nm kg −1 and the Antarctic Bottom Water 100 to 106 nm kg −1. Both barium and silica behave non-conservatively in basins with restricted circulation—the Greenland and Norwegian seas and the Angola Basin—with anomalies of up to 1, 2 and 7 nm Ba kg −1, respectively. There is extensive in situ production of silica and barium in the bottom waters of the Weddell Sea Basin, the silica anomaly ranging up to 35 μm kg −1 and that for barium to 15 nm kg −1. Barium behaves uniquely only in the upper waters. At tropical and temperate latitudes there is commonly a minimum of several nannomoles per kilogram in the uppermost thermocline, often associated with the high salinity core of the Sub-Tropical Underwater. In the Circumpolar Current the depletion in surface silica is associated with only a minor reduction in barium. The values at <5 μm Si kg −1 are about 30 nm kg −1 higher than those at lower latitudes. The important question of the removal mechanism is not resolved from the profile data.