Volume 19, Issue 6, November 2001
- regular articles
- brief reports and comments
- rapid communications
- papers from the 45th international conference on electron, ion, and photon beam technology and nanofabrication
- optical lithography
- euv lithography
- x-ray lithography
- electron beam lithography
- ion beam technology
- sources and optics
- mask technology
- resist technology
- nanofabrication and nanodevices
- imprint lithography
- mems and biological applications
- alignment and metrology
- dry etching
Index of content:
- REGULAR ARTICLES
Investigation of molecular beam epitaxial heterostructures by atomic force microscopy and x-ray diffractometry19(2001); http://dx.doi.org/10.1116/1.1409388View Description Hide Description
layers were grown on Si(111) substrates at 400, 550, and 700 °C by molecular beam epitaxy. The surface morphology observations by atomic force microscopy indicated that the layers on Si(111) substrates grew as islands associated with screw dislocations, which coalesced less densely at higher growth temperatures. The layers grown at higher temperatures were more susceptible to formation of microcracks due to larger mismatch of the thermal expansion coefficient. The orientational relationship between layers and Si(111) substrates was confirmed to be by x-ray diffraction measurement. As a function of growth temperature and layer thickness, the crystallinity of resulting layers in terms of full width at half maximum values was investigated. In particular, for layers grown at a high temperature of 700 °C, lattice relaxation and crystallinity degradation with layer thickening were found.
19(2001); http://dx.doi.org/10.1116/1.1409391View Description Hide Description
The use of surface monolayer initiated polymerization, in which initiators are chemically bound to a surface, can generate robust barrier polymers for pattern formation in silicon by reactive ion etching. The combination of poly(vinylarenes) and a new surface initiator based upon a phenylazo initiator provides excellent etch resistance and superior performance.
19(2001); http://dx.doi.org/10.1116/1.1409392View Description Hide Description
Reactive ion etching with sulfur hexafluoride gas has been employed to create deep structures in bulk samples of the piezoelectric material lead zirconate titanate, is chosen for compatibility with dry etching of silicon with a possibility for production of hybrid silicon-piezoelectric devices. Thick photoresist layers have been used to pattern PZT to a depth of 2 μm at a rate of The use of more durable nickel masks, formed by electroplating through the thick resist, leads to structures greater than 100 μm in height, with an average sidewall angle of ∼72°. The profile of the deep PZT structures is seen to depend on etch duration and the spacing of structures, attributed to the redeposition of mask and etch products, respectively. The addition of nitrogen and argon to the plasma is shown to produce small improvements in the profiles. By combining gas addition with heating of the substrate PZT etch rates up to have been obtained.
Materials aspects, electrical performance, and scalability of Ni silicide towards sub-0.13 μm technologies19(2001); http://dx.doi.org/10.1116/1.1409389View Description Hide Description
Ni-silicide phase formation with and without a Ti capping layer was studied by sheet resistance,x-ray diffraction and transmission electron microscopy.Ni monosilicide is found to be the stable phase in a temperature range from 400 to 600 °C. At lower temperatures the phase is found to be present. For temperatures higher than 700 °C NiSi is converted into Pyramidal precipitates were found to grow epitaxially along the Si〈111〉 planes for annealing temperatures as low as 310 °C. The epitaxial grains were found to disappear when the annealing temperature is increased. Stress buildup during Ni silicidation was measured in situ and could be correlated to the formation of the different Ni-silicide phases. The stress induced by Ni-monosilicide formation compares favorably to the stress induced by Co disilicide and Ti disilicide. The average silicon consumption required to obtain a certain sheet resistance was found to be 35% lower for Ni monosilicide compared for Co disilicide. It was found that a two-step process is needed to obtain complete conversion to the preferred Ni-monosilicide phase without lateral silicide growth. The sheet resistance of Ni-silicided narrow poly-Si and active area lines was found to be low, even when Ni silicide was formed without a Ti cap. No degradation of the Ni silicide on the narrow poly-Si lines was observed when the silicidation temperature was increased to 600 °C. The reverse bias leakage of shallow Ni-silicided and Co-silicided square diodes was compared for varying junction depths and varying silicide thicknesses. For similar junction depth and similar sheet resistance, a lower reverse bias leakage current was obtained for a Ni-silicided junction compared to its Co-silicided counterpart. This may be attributed to the reduced Si consumption of Ni monosilicide compared to Co disilicide.
19(2001); http://dx.doi.org/10.1116/1.1409390View Description Hide Description
The reduced brightness for a 〈100〉 ZrO/W Schottky electron emitter with a tip radius of 0.8 μm has been measured. The maximum reduced brightness measured was The measurements of the reduced brightness are compared with the extended Schottky theory and the theory on stochastic Coulomb interactions. At high angular current densities the reduced brightness is limited by statistical Coulomb interactions in the gun lens region. The limits to the maximum reduced brightness in an ideal configuration are explored and found to be for a 0.2 μm tip and a current limiting aperture in the extractor electrode.
Experimental conditions for a highly ordered monolayer of gold nanoparticles fabricated by the Langmuir–Blodgett method19(2001); http://dx.doi.org/10.1116/1.1410943View Description Hide Description
A highly ordered monolayerfilm of alkanethiol-encapsulated goldnanoparticles was fabricated on a silicon substrate by using the Langmuir–Blodgett (LB) method. The effects on the particle order, of the particle concentration and the type of solvent of the LB spreading suspension of encapsulated gold particles, were studied. We found that a low particle concentration of 0.06–0.3 mg/mL in chloroform is optimal for the fabrication of high quality gold particle monolayers. Since the proposed method is not restricted to gold particles, it is believed to be a practical process for fabricatingquantum dot structures of various particle sizes and compositions.
19(2001); http://dx.doi.org/10.1116/1.1410944View Description Hide Description
Impacts of energetic argon ion clusters on surfaces of inorganic solids have shown modification of the respective surface properties. Polymeric samples such as (PC) polycarbonate and (PP) polypropylene were irradiated by argon ion clusters (average size of 3000 atoms) accelerated to 10 and 20 keV at doses ranging from to The irradiatedsurfaces were investigated by surfometer (profilometer), atomic force microscope, contact angle measurements and x-photoelectron spectroscopy. Measurements using these techniques show that the smoothing effect and the postirradiation oxidation of the surface take place. The direct evidence was obtained in case of PP that the irradiation dose produces the smoothest surface as measured by surfometer. In the case of PC the same conclusion is suggested indirectly.
19(2001); http://dx.doi.org/10.1116/1.1410942View Description Hide Description
The differences in valence band structure and work function between heteroepitaxial nanocrystals and the surrounding substrate were measured with a spectroscopic photoemission and low energy electron microscope which allows laterally resolved photoemission spectroscopy. The nanocrystals were obtained by depositing nominally 2 and 4 monolayers (ML) of InAs on a Se-terminated GaAs(001) surface. The samples showed differences in the valence band edge energy and work function both between nanocrystals and substrate as well as between 2 and 4 ML. We suggest that Se termination of the nanocrystals is the reason for these differences.
Chemical composition, morphology, and deep level electronic states of GaN (0001) (1×1) surfaces prepared by indium decapping19(2001); http://dx.doi.org/10.1116/1.1412656View Description Hide Description
Ordered GaN (0001) (1×1) surfaces are prepared after removal from the growth chamber via thermal desorption of a thin In cap layer at 650 °C in combination with one thermal flash of Ga metal to reduce residual O and C contamination. Auger electron spectroscopy(AES) and low energy electron-excited nanoscale luminescence (LEEN) spectroscopy results show that In can prevent contamination during atmospheric exposure if it can cover the surface uniformly. LEEN spectra of the ordered surface show that the In capping layer is desorbed from the GaN without reacting to produce or diffusing into the GaN to produce new localized states. Subsequent atomic force microscopy(AFM) measurements reveal an atomically smooth film plus Ga droplets residual to the flash annealing. These results suggest that In decapping may be useful in obtaining clean, LEED-ordered GaNsurfaces after transport in air with a minimum of UHV treatment.
Improvement of the interface characteristics by two-step deposition with intermediate plasma treatment using gas19(2001); http://dx.doi.org/10.1116/1.1412657View Description Hide Description
We studied two-step deposition with an intermediate plasma treatment to improve the interfacecharacteristics. Using this method, we can minimize the plasma damage on the Si surface and improve the interfacecharacteristics such as intermediate oxidation states, interface trap density and shift. The interfacecharacteristics were improved with the intermediate plasma treatment after a 6 nm first oxide deposition. The number of Si atoms in the suboxide region, compared with the sample without plasma treatment, was decreased 14.7% and a sixfold ring structure became dominant. Interface trap density was decreased from to by the oxygen incorporation in the transition region. The moderate oxygen incorporation near the interface reduced the shift due to the decrease of the fixed oxide charge.
19(2001); http://dx.doi.org/10.1116/1.1412658View Description Hide Description
We describe a technique for ultra-high-vacuum compatible deposition of structures on flat substrates. This technique allows one to form micrometer and even submicron-sized structures on a flat surface with minimal contamination. It also has the advantage of producing a smooth edge profile similar to those achieved using a two-layered resist.
19(2001); http://dx.doi.org/10.1116/1.1414016View Description Hide Description
Some of the important areas to be improved for lithography simulation are: obtaining correct exposure parameters and determining the change of refractive index. It is known that the real and imaginary refractive indices are changed during exposure. We obtained these refractive index changes during exposure for 193 nm chemically amplified resists. The variations of the transmittance as well as the resist thickness were measured during ArF excimer laser exposure. We found that the refractive index change is directly related to the concentration of the photo acid generator and deprotected resin. It is important to know the exact values of acid concentration from the exposure parameters since a small difference in acid concentration magnifies the variation in the amplified deprotection during postexposure bake. We developed and used a method to extract Dill exposure parameters for 193 nm chemically amplified resist from the refractive index change upon exposure.
19(2001); http://dx.doi.org/10.1116/1.1414116View Description Hide Description
Recent advances in ultralarge-scale integration have typically depended on reductions in etched feature size. This has motivated efforts to find etch processes that will precisely etch increasingly smaller features while retaining the ability to etch larger features. As feature sizes push below 0.25 μm, reactive ion etch (RIE) lag control becomes increasingly important. Knowing how RIE lag scales with feature size for a given process aids in determining if that process must be discarded and a new one developed. In those situations where a process cannot be discarded, an understanding of RIE lag scaling aids in predicting fabrication difficulties for a given device design. Using a minimal set of initial assumptions, it is shown that a relationship can be derived which relates etch rate to the time development of the feature aspect ratio. It is then shown that this relationship can be used to derive an expression for the etch depth as a function of time and feature size. The assumptions made are justified by phenomenological observation rather than by an assumed mechanism. This approach enhances the generality of the results obtained, thus making them useful for a variety of practical etch engineering applications.
19(2001); http://dx.doi.org/10.1116/1.1414118View Description Hide Description
Initial reactions for molecules at the surface have been investigated by using a supersonic molecular-beam scattering technique. Results with a high corrugation surface indicate a complex, dynamical behavior of molecules interacting with the surface. A fine chemisorption probability measurement at an incident translational energy of 0.12 eV suggests an extremely fast dissociative chemisorption process with an initial probability of Angular distributions measured for scattered molecules at 0.06, 0.12, and 1.45 eV strongly indicate three channels of behavior: inelastic direct scattering, trapping/desorption, and multiple scattering. In particular, the multiple scattering channel arises from the corrugation of the surface.
19(2001); http://dx.doi.org/10.1116/1.1414113View Description Hide Description
This article reports an original technique for measuring the flexural resonance response of optical fibers of around 1 mm in length considered as atomic force microscope cantilevers. This technique was found particularly suitable for precisely investigating the effect of aging of optical fibers due to external factors such as temperature, action of hydrogen, or ionic aggressive solutions. Compared to the corresponding atomic force microscopy images, the measurement of the resonance frequency shift leads to the determination of two factors characteristic of the surface reactivity of the fiber: first, the decrease in frequency that can be considered in terms of mass loading, and second both the frequency increase and the loss in Q factor resulting from the variation of the Young modulus and the internal friction of the fiber.
19(2001); http://dx.doi.org/10.1116/1.1414114View Description Hide Description
Global pattern density effects on aluminum alloy etching were quantitatively analyzed for sub-0.25 μm technology logic devices. We found that etching the metal layer with one pattern density while applying the plasma activation parameters optimized for the other pattern density often results in inferior performance, even if the minimum design rules of both layers are the same. Additional studies show that the aluminumetch rate has an almost linear relationship to the pattern density of the etched metal layer when all the activation parameters are fixed. This evokes the necessity that the plasma activation parameters be optimized properly with the pattern density of each metal layer as well as with the minimum design rule. We speculate that these pattern density effects are caused by the variation of etching environment that is solely determined by effective etchants density and their effective residence time. Thus it may be possible to alleviate the global pattern density effects by controlling the plasma activation parameters in such a way that these two effective values are independent of the pattern density. Based on the aforementioned speculation we controlled total pressure and feed gas flow rate and were able to achieve stable etching performance independent of the global pattern density.
19(2001); http://dx.doi.org/10.1116/1.1414050View Description Hide Description
The origins of fluorine in dry ultrathin silicon oxides (<1 nm) were investigated as the incorporation of fluorine in these layers may improve their reliability and interface quality. Oxides were grown at room temperature (RT) by in an integrated tool combining vapor HF surface preparation and oxide growth in a single chamber. The chemical composition and thickness of the layers were characterized by x-ray photoelectron spectroscopy. It is shown that incorporation of fluorine in these oxides originated mainly from the contamination of the tool (dead spaces and surfaceadsorption) and from the fluorine left at the wafer surface by the in situ HF process. The levels of these sources of fluorine were about two orders of magnitude higher than from a wet HF dip. No evidence was found for the existence of subsurface fluorine [Kasi et al., Appl. Phys. Lett. 58, 2975 (1991)] as oxides grown in a separate noncontaminated cell 1 atm RT to 200 °C) did not show any significant increase in fluorine content as a function of oxide thickness. Hence the amount of fluorine incorporated into oxides grown in cluster tools under similar conditions will depend not only on the method selected for surface preparation but also on whether surface preparation and oxidation are performed in the same chamber or not. The possible benefits of determined fluorine levels are discussed.
Investigation of the bonding strength and interface current of wafers bonded by surface activated bonding at room temperature19(2001); http://dx.doi.org/10.1116/1.1414115View Description Hide Description
Equivalent bulk strength of the interface between bonded through the surface activated bonding (SAB) method is found. The interface current was extensively investigated. Nonideal behavior of the junction current is found to be due to the tunneling current between the conduction band and valence band across the transition region associated with band gap states. Interface current decreases with increasing sputtering time and energy and vice versa. Irradiation time and energy dependent behavior indicates that the accumulation of radiation induced defects associated with the doping controls the interface current of Moreover, strong impact of the exposure to an ultrahigh vacuum atmosphere of the activated surfaces on the interface current of is found. Finally it can be suggested that a laser diode can be fabricated by the bonding between and through the SAB method, because of the achievement of equivalent bulk strength of the interface.
19(2001); http://dx.doi.org/10.1116/1.1415516View Description Hide Description
A new metamorphic high electron mobility transistor(HEMT) structure was grown on a GaAs substrate with a graded buffer layer by solid-source molecular beam epitaxy. The channel layer was grown on the InGaP buffer layer directly without an InAlAs buffer as in the conventional design. High-resolution x-ray diffraction reveals that the whole layer structure is nearly fully relaxed. Hall measurement showed that this new layer design exhibits higher electron mobility and carrier concentration as well as lower light sensitivity compared to the reference sample with the conventional design. The promising device performance demonstrates the potential of using this metamorphic HEMT device in high speed and high frequency applications.
In situ measurement of aspect ratio dependent etch rates of polysilicon in an inductively coupled fluorine plasma19(2001); http://dx.doi.org/10.1116/1.1415514View Description Hide Description
The etch rate of polysilicon in high aspect ratio structures has been studied in an inductively coupled fluorine based plasma (pure The change of the siliconetch rate with increasing aspect ratio [aspect ratio dependent etch rate or reactive ion etching (RIE) lag] has been measuredin situ by interferometry. The experimental structures as well as the process conditions were chosen such that (i) the interaction of neutral fluorine atoms with the siliconsurface determines the etch rate, (ii) the ion energy is minimized, (iii) the mass transport of neutrals is in a molecular flow (Knudsen) regime, and (iv) the interaction of the etch species with the sidewalls can be neglected. Under these conditions, the experimental findings indicate that the RIE lag effect is reduced for higher pressures and lower cathode temperatures, i.e., for higher fluorine atom coverages of the siliconsurface. This is in agreement with the Knudsen transport model by Coburn and Winters [W. Coburn and H. F. Winters, Appl. Phys. Lett. 55, 2730 (1989)]. Probabilities for the reaction of fluorine atoms with the siliconsurface between 0.03 and 0.11 can be derived when fitting the experimental data with this model. The findings reported in this work are of relevance for the formation of deep trench storage capacitors and polysilicon plugs. In particular, we show that we can control RIE lag and etch rate independently for the given process conditions.