L. E. Trimble

Catalytic effect of SiO on thermomigration of impurities in SiO2

We have found that encapsulated thin Si films, adjacent to SiO2, are dissolved at elevated temperatures by a reaction: Si+SiO2→2SiO, with SiO diffusing through the silica network. The presence of SiO in SiO2 in a concentration ≤3 at. % has a profound effect on thermomigration of dopant impurities in the oxide. We propose a model for transport of As‐, Sb‐, P‐, and Ge‐rich precipitates, 50–1000 A in diameter, based on a reaction between SiO2 and the precipitates that is mediated by a catalytic influence of SiO molecules. Only in the presence of SiO are the bonds in the SiO2 network broken ahead of the drifting clusters and regrown behind them. The model predicts that the migration of precipitates is controlled by diffusivity of SiO in silica, consistent with the narrow range of drift velocities for clusters of different chemical compositions. The data also suggest that SiO2 dissociation at the Si/SiO2 interface is diffusion limited, which explains why decomposition of thin SiO2 in vacuum is spatially inhomo...

Thin‐film waveguide magneto‐optic isolator

A thin‐film waveguide Faraday rotator which provides nonreciprocal polarization rotation of ±45° for light of wavelength 1.45 μm with an extinction ratio of 500:1 has been demonstrated. This isolator structure makes use of laser annealing to reverse the sublattice magnetization and hence the sign of the Faraday effect in localized regions of a (Bi, Ga) yttrium iron garnet film. A novel geometrical pattern was designed for these regions to overcome the effects of the inherent thin‐film birefringence.

Seeded oscillatory growth of Si over SiO2 by cw laser irradiation

Extensive seeded epitaxial growth of crystalline Si over SiO2 was achieved by an oscillatory regrowth method applied to rectangular Si pads recessed into a thick SiO2 film. Narrow (≃5 μm) via holes linked the pads with the bulk (100) Si substrate. Oriented single crystals propagated as far as 500 μm from the seeding area, following the long term advance of a scanned focused laser beam.

Ultra-fast (0.5- mu m) CMOS circuits in fully depleted SOI films

CMOS dual-modulus, divide by 128/129, prescaler circuits were built in thin Si films on SIMOX (separation by implantation of oxygen) wafers. They operated at 6.2 GHz, which is 50% faster than control circuits built in bulk Si. Detailed electrical characterization of individual n- and p-channel transistors was performed. The capacitances for the n and p diodes were also measured. Using these data in circuit simulations, it was determined that the gain in speed was primarily due to the decrease in the parasitic capacitances, in particular that of the source/drain junctions. Also measured were the ring-oscillator delay times, with a minimum delay per stage of 34 ps. >

Spatial melt instabilities in radiatively melted crystalline silicon

Strongly nonplanar melting of polished and oxidized single crystalline silicon heated by intense incoherent light is reported. Although irradiation is uniform, the surface breaks up into an array of distinctly faceted molten segments separated by solid unmelted regions. The melt depth can have a sawtooth appearance and is always nonuniform. We show that initiation of melting at discrete sites must be caused by the presence of a nucleation barrier and that the phase coexistence is sustained because of the difference in light coupling to the solid and to the liquid Si. Faceting of the molten regions is then a simple, although rarely observed, consequence of melting from inside the crystal. We also show that phase coexistence at the irradiated surface assures steady‐state heat flow in the samples over a wide range of input powers.

Magneto-optic waveguide isolators based on laser annealed (Bi, Ga) YIG films

To overcome the effects of linear birefringence which limits the Faraday rotation achievable in magneto-optic thin film waveguides, a novel geometrical pattern of Faraday effect reversals has been designed. This pattern of P/2 segments followed by a P/4 segment where P is the birefringent period, has been built permanently into a (Bi,Ga)YIG film, with composition close to the compensation point, by laser annealing. This film provides nonreciprocal rotation of ±45° for light of wavelength 1.45 μm with an extinction ratio of 500 to 1, corresponding to 27 db of isolation.

Tungsten patterning for 1:1 x‐ray masks

A subtractive process to form subhalf micron, vertical‐walled patterns in half‐micron thick tungsten on x‐ray masks has been developed. Electron‐beam lithography was used to form resist patterns on a structure consisting of 300 A Cr on 5000 A W on 200 A Cr on an approximately 1 μm thick poly‐silicon or silicon nitride membrane. The Cr masking and etch‐stop layers above and below the W layer are required because the resist and membrane materials etch rapidly in fluorine based W etching plasmas. Chromium was chosen for these layers because it has a high selectivity in the W etch (≊40:1), is compatible with the W deposition process, and can be patterned in an O2–Cl2 plasma which does not etch W or the membrane materials. Helium backside cooling at a pressure from 1 to 5 Torr controls membrane temperature during all plasma processing steps. Pure CBrF3 or CHF3 etch W slowly while simultaneously depositing polymer which produces sloping profiles where the base of the feature is wider than the initial mask width...

Ultra-high speed CMOS circuits in thin SIMOX films

CMOS dual-modulus prescaler circuits were built in very thin SIMOX films. They operate at 6.2 GHz, the highest speed ever reported for a digital CMOS circuit and 50% faster than the control circuits built in bulk Si. The high speed is obtained by taking advantage of the intrinsic properties of the SOI (silicon-on-insulator) structure combined with the symmetric CMOS technology that simultaneously optimizes the characteristics of both the p- and n-channel transistors.<<ETX>>

High‐temperature stability of Si/SiO2 interfaces and the influence of SiO flux on thermomigration of impurities in SiO2

We analyze experimentally unidirectional mass transport of As implanted into a SiO2 film covered with Si and heated to 1405 °C in a temperature gradient. The data can only be explained if we postulate that the thermomigration process is mediated by a flux of SiO molecules, flowing from the Si/SiO2 interfaces into the oxide. From the delay times before the onset of As drift, we estimate diffusivity of SiO at ∼4×10−13 cm2 /s at 1405 °C. The data also explain the apparent dichotomy between high‐temperature dissociation of SiO2 , measured experimentally and predicted by thermodynamic arguments, and the ability to heat Si‐coated SiO2 up to the melting point of Si at 1412 °C without any loss of the oxide integrity. The latter is possible because coated SiO2 saturates with SiO, resulting in steady‐state conditions.

Precipitation of group V elements and Ge in SiO2 and their drift in a temperature gradient

It is shown that P, Sb, and Ge ions implanted in SiO2 precipitate into spherical clusters of up to 1000 A diameter when heat treated in an oxygen‐free ambient. This behavior is similar to that reported earlier for As implants. The clusters can be detected directly by transmission electron microscopy, or inferred from the unidirectional drift of the doped zone in a temperature gradient. Boron, a representative of group III, is the only element among those tested that does not migrate in a ∇T, suggesting the absence of phase separation.