Y. Horiike

Digital etching study and fabrication of fine Si lines and dots

Abstract For the goal of damage-free microfabrication, digital etching in which one or a few atomic layers are removed with minimum reaction energy has been studied. The atomic layer etching of Si(100) was achieved by the precise control of F atom adsorption. To evaluate sidewall etching damage, conductance for lines fabricated on SIMOX was measured at 4.2 K. Lines fabricated by the digital method exhibited no appreciable damage, contrary to the 0.2 μm line fabricated by magnetron reactive ion etching. In a 0.1 μm line subjected partly to an exposure of hydrogen plasma, non-linearity in the I–V relationship was observed at 4.2 K. The fabrication of Si dots with 20–100 nm diameter was successfully achieved by both an adequate electron beam dose and Ar+ irradiation time. Photoluminescence measurements revealed that a significant plastic deformation was generated in oxidized Si dots on SIMOX substrate.

Digital chemical vapor deposition of SiO2

The repetitive cycles of a few monolayers hydrogenated silicon deposition and its oxidation has been employed for the growth of SiO2. The surface reaction is promoted by an alternate irradiation of silicon hydride radical beam produced by the upstream pulsed microwave discharge of SiH4 and discharged oxygen beam. The deposition rate is controlled by the flow velocity of silane gas jet and substrate temperature. It is shown that the deposition species ejected with supersonic velocity into a high vacuum reactor conformably fills the SiO2 film into a deep Si trench.

Filling of Si oxide into a deep trench using digital CVD method

Abstract To fill a high-quality SiO 2 film into a deep trench, digital CVD was carried out by repeating a cycle of conformable deposition of Si-like films; then its oxidation was studied. After investigating the reaction of TMS (trimethylsilane) and TES (triethylsilane) with oxygen radicals, it was found that the extraction reaction of hydrogen in TES with hydrogen radicals realized CVD of a film with excellent step coverage for 60% H 2 in TES at 250°C. The feature is considered to result from the high-viscosity nature of the film which includes C x H y groups produced by the dominant surface reaction between TES and hydrogen radicals. Eventually, the layer-by-layer technique has been applied to oxidizing C x H y groups. Hydrogen and oxygen radicals which were generated by remote H 2 and O 2 plasma were introduced intermittently. Hence, conformable CVD of the SiO 2 film has been realized. The SiO 2 film was deposited at 250°C with an initial thickness per cycle of 5 A at 1 s oxygen pulse. This film offered a low concentration of organic species, thus a relatively low BHF etch rate.

Electromigration Characteristics of Cu and Al Interconnections

Electromigration activation energies (Ea) of Al and Cu interconnections are strongly dependent on the grain boundary morphology, and it is pointed out that Ea of bamboo-like Al interconnection is not less than Ea of small grain Cu interconnections. Small resistance oscillatory changes caused by electromigration, which are classified into three categories; oscillation, downward spikes, and upward spikes, are investigated in detail. It seems most likely that oscillations correspond to annihilation and formation of the one void. It is also pointed out that downward spikes are local, while upward spikes are non-local. Dislocation dynamics such as generation, rapid transport and subsequent annihilation are considered to be origins of spikes.

Sheath Width in Negative-Ion-Containing Plasma

Sheath width in negative-ion-containing plasma, which is important in plasma etching, is numerically investigated on the basis of Poissons equation. With the aid of the previously reported Bohm criterion voltage, the negative ion term is consistently incorporated into the sheath equation. One of the important findings is that the sheath width increases with an increase in the negative ion density. This is simply because the positive-ion current decreases with negative-ion density even under the condition of a constant plasma density. The positive-ion density in the sheath front must decrease to keep neutrality with negative charges when the negative ions with low temperature are introduced, provided that the Bohm criterion voltage is not greatly different.

Fabrication and Evaluation of Three-Dimensional Optically Coupled Common Memory

A three-dimensional optically coupled common memory (3D-OCC memory) test chip, on which GaAs LEDs are integrated using the microbonding technique, has been fabricated using a 2 µ m complementary metal-oxide-semiconductor (CMOS) technology. Static memory cell circuits with photodiodes were formed on the chip. Optical writing and electrical reading operations of the 3D-OCC memory test chip have been demonstrated.

Vertical and lateral hole aluminum filling characteristics employing electron cyclotron resonance plasma sputtering with high magnetic field

Filling of submicrometer vertical and lateral holes was investigated by employing ECR (electron cyclotron resonance) aluminum sputtering with two times higher magnetic field than the usual condition of 875 G. Deep submicron contact holes with no adhesive metal layer were satisfactorily filled at 350u2009°C, which was a much lower temperature than conventional methods. Buried lateral trenches with 1‐μm depth were also completely filled at 300u2009°C. The filling mechanism is considered to be a cooperative effect of an enhanced diffusion by an ion bombardment effect, and the formation of dense aluminum islands at the inner wall which act as an adhesive layer.

Observation of human chromosome fibers in a water layer by laser-plasma x-ray contact microscopy

Soft x-ray contact microscopy was applied to hydrated human chromosomes. Chromosomes of human lymphocytes were spread on a clean surface of distilled water, attached on an x-ray resist, polymethylmethacrylate (PMMA), immediately covered with a silicon nitride window, and mounted in a simple hydrated chamber. The specimens were exposed to a single shot of laser-produced gold plasma x rays (600 ps) in a vacuum chamber. The developed images were observed with transmission electron microscope using the replica method with a plasma polymerization-film in a glow discharge. The results show that we have imaged the complicated entanglement of chromosome fibers in a hydrated condition. The thickness was estimated as 10 nm in an average of four narrow parts of these fibers. Particle like structures were observed in many places. The present results prove that a hydrated biological specimen is observable with the contrast produced by its components themselves using soft x-ray microscopy at the resolution of 10 nm. During this imaging exposure, however, the silicon nitride (SiN) window was broken. We have studied the reason for this evidence and found that the energy absorbed by the SiN window or water layer was very high. The estimated temperature increase was 870 -1470 degree(s)C for SiN and 43 degree(s)C for the water layer. These results suggest that the temperature increase may be responsible for the breakage of SiN window.

High intensity hydrogen lamp employing helicon wave plasma and its application to Si and SiO2 etching

Abstract A high intensity hydrogen Lyman α, H α (10.2 eV) employing helicon wave plasma has been studied as a VUV light source and applied to Si and SiO 2 etching. NF 3 was highly dissociated by H α irradiation at higher pressure, while the Si etch rate dropped rapidly with distance from the window due to recombination loss of fluorine atoms. An anisotropic etching of n + poly-Si under VUV irradiation was achieved. This may be performed by dominant photo-etching of altered layers generated as a result of reaction of Cl atoms with phosphorus atoms. However, details are not understood well.

Digital Process for advanced VLSI's and Surface Reaction Study

Digital etching was carried out by repeating the fundamental reaction cycles of adsorption, reaction and desorption for fluorine(F) or chlorine(Cl)/Si systems. In the F/Si case, atomic layer etching of Si(100) was achieved by adsorption of F atoms produced by a remote discharge of F 2 /99.8%He on the cooled Si surface and subsequent Ar* ion (≅20eV) irradiation. The digital method revealed that the cryogenic etching occurred by ion bombardment on physiosorbed F atoms on the cooled Si surface. Adsorption of Cl atoms on Si at room temperature allowed self-limiting reaction with etch rate of 0.4 A/cycle. The etching increased rapidly over 40 V of substrate voltage. Secondly, reaction of TES (triethylsilane) with hydrogen(H) atoms was also found to lead to conformal CVD (Chemical Vapor Deposition) of Si film involving organic species. Then Si oxide and nitride films were formed by digital CVD which repeated a cycle of first deposition of this film and subsequent its oxidation and nitridation. The electrically excellent multilayer stacked oxide and nitride film was filled in to deep trench. Insitu FTIR-ATR spectroscopy demonstrated that the surface reaction was predominant for the TES/H process.