Surface Binding States Research Articles

Effect of Cl2 Radical on Dry Development of Spin-Coated Metal Oxide Resist.

In this study, the effects of Cl2 radicals on dry development of spin-coated metal oxide resist (MOR) and changes in its surface binding states were investigated to verify the mechanism of dry development. Dry development characteristics of tin hydroxide (Tin OH), which is one of the MOR candidates for next generation lithography, were investigated as functions of process time and temperature using a Cl2 radicals source. Non-UV-exposed Tin OH film showed a linear etch rate (1.77 nm/min) from the initial thickness of ∼50 nm, while the UV-exposed film showed slower etch behavior (1.46 nm/min) in addition to the increase of film thickness for up to 3 min during the Cl2 radical dry development. UV-exposed photoresist (PR) contained more oxygen (Sn-O bonding) in the film due to the removal of butyl compounds from the clusters during the UV exposure process. Therefore, due to the lower reaction of chlorine radicals with Sn-O in the UV-exposed Tin OH than the other bindings, the non-UV-exposed PR was preferentially removed compared to the UV-exposed PR. As the temperature decreases, the overall etch rate decreases, but the difference in etch rate between exposed and unexposed Tin OH becomes larger. Finally, at a substrate temperature of -20 °C, the non-UV-exposed Tin OH with a thickness of 50 nm was completely removed, while ∼30 nm thick PR remained for UV-exposed Tin OH. Eventually, a negative tone development was possible with Cl2 radical plasma due to the difference in activation energy between the UV-exposed and non-UV-exposed films. It is believed that dry development using Cl2 radicals will be one of the most important process techniques for next-generation patterning to remove problems such as pattern leaning, line edge roughness, residue, etc., caused by wet development.

A Quantitative Model for cAMP Binding to the Binding Domain of MloK1

Ligand-protein binding processes are essential in biological systems. A well-studied system is the binding of cyclic adenosine monophosphate to the cyclic nucleotide binding domain of the bacterial potassium channel MloK1. Strikingly, the measured on-rate for cyclic adenosine monophosphate binding is two orders of magnitude slower than a simple Smoluchowski diffusion model would suggest. To resolve this discrepancy and to characterize the ligand-binding path in structural and energetic terms, we calculated 1100 ligand-binding molecular dynamics trajectories and tested two scenarios: In the first scenario, the ligand transiently binds to the protein surface and then diffuses along the surface into the binding site. In the second scenario, only ligands that reach the protein surface in the vicinity of the binding site proceed into the binding site. Here, a binding funnel, which increasingly confines the translational as well as the rotational degrees of freedom, determines the binding pathways and limits the on-rate. From the simulations, we identified five surface binding states and calculated the rates between these surface binding states, the binding site, and the bulk. We find that the transient binding of the ligands to the surface binding states does not affect the on-rate, such that this effect alone cannot explain the observed low on-rate. Rather, by quantifying the translational and rotational degrees of freedom and by calculating the binding committor, our simulations confirmed the existence of a binding funnel as the main bottleneck. Direct binding via the binding funnel dominates the binding kinetics, and only ∼10% of all ligands proceed via the surface into the binding site. The simulations further predict an on-rate between 15 and 40μs−1(mol/l)−1, which agrees with the measured on-rate.

Phase transition kinetics and surface binding states of methylammonium lead iodide perovskite.

We have presented a detailed analysis of the phase transition kinetics and binding energy states of solution processed methylammonium lead iodide (MAPbI3) thin films prepared at ambient conditions and annealed at different elevated temperatures. It is the processing temperature and environmental conditions that predominantly control the crystal structure and surface morphology of MAPbI3 thin films. The structural transformation from tetragonal to cubic occurs at 60 °C with a 30 minute annealing time while the 10 minute annealed films posses a tetragonal crystal structure. The transformed phase is greatly intact even at the higher annealing temperature of 150 °C and after a time of 2 hours. The charge transfer interaction between the Pb 4f and I 3d oxidation states is quantified using XPS.

Etching Characteristics of ZnO and Al-Doped ZnO in Inductively Coupled Cl2/CH4/H2/Ar and BCl3/CH4/H2/Ar Plasmas

ZnO and Al-doped ZnO (AZO) were etched in Cl2/CH4/H2/Ar (Cl2-based) and BCl3/CH4/H2/Ar (BCl3-based), inductively coupled plasmas (ICPs) and their etching characteristics were compared by varying the Cl2/(Cl2+CH4) and BCl3/(BCl3+CH4) flow ratios, top electrode power and dc self-bias voltage (Vdc). The etch rates of both ZnO and AZO layers were higher in the Cl2-based chemistry than in the BCl3-based chemistry. The AZO and ZnO etch rates were increased and decreased, respectively, with increasing Cl2 or BCl3 flow ratio. Optical emission measurements of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, indicated that, with increasing Cl2 or BCl3 flow ratio; the effective removal of Al in the AZO enhanced the AZO etch rate, whereas the reduced removal of Zn by the Zn(CHx)y products reduced the ZnO etch rate.

Effect of doping elements on ZnO etching characteristics with CH 4/H 2/Ar plasma

Effect of doping elements on the etching characteristics of doped-ZnO (Ag, Li, and Al) thin films, etched with a positive photoresist (PR) mask, and an etch process window for infinite etch selectivity were investigated by varying the CH 4 flow ratio and self-bias voltage, V dc, in inductively coupled CH 4/H 2/Ar plasmas. Increased doping of ZnO films decreased the etch rates significantly presumably due to lower volatility of reaction by-products of doped Li, Ag, and Al in CH 4/H 2/Ar plasmas. The etch rate of AZO (Al-doped ZnO) was most significantly decreased as the doping concentration is increased from 4 to 10 wt%. It was found that process window for infinite etch selectivity of the doped ZnO to the PR is closely related to a balance between deposition and removal processes of a-C:H (amorphous hydrogenated carbon) layer on the doped-ZnO surface. Measurements of optical emission of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, implied that the chemical reaction of CH radicals with Zn atoms in doped-ZnO play an important role in determining the doped-ZnO etch rate together with an ion-enhanced removal mechanism of a-C:H layer as well as Zn(CH x) y etch by-products.

Investigation of process window during dry etching of ZnO thin films by CH4–H2–Ar inductively coupled plasma

The etching characteristics of ZnO thin films, etched with a positive photoresist mask and a process window in inductively coupled CH4–H2–Ar plasmas were investigated by varying the various process parameters. It was found that the process window for ZnO etching is closely related to the balance between the deposition and removal processes of the a-C:H (amorphous hydrogenated carbon) layer on the ZnO surface. Under certain conditions, the etch rate selectivity of ZnO to PR is infinite, because the ZnO films continue to be etched, but a net deposition of the a-C:H polymer occurs on the top of the photoresist. The measurements of the radical species in the plasma and the surface binding states by optical emission spectroscopy (OES) and x-ray photoelectron spectroscopy (XPS), respectively, revealed that the chemical reaction of the CH radicals with the Zn atoms in ZnO and the ion-enhanced removal mechanism of the a-C:H layer play an important role in determining the ZnO etch rate, as well as the etch by-products.

Characterization of oxide etching and wafer cleaning using vapor phase anhydrous hydrofluoric acid and ozone

Abstract A cleaning process using anhydrous hydrofluoric acid/methanol (AHF) and ozone was carried out in a vapor phase cleaning module (VPC). The dependence of the AHF vapor phase etch rate of thermally grown silicon dioxide on different process parameters, such as etch time, AHF-flow and temperature was studied. The optimized etch process is attained at a temperature of 40°C and a pressure of 50 mbar. To demonstrate the feasibility of this cluster tool for advanced gate dielectric formation, investigations on surface properties after AHF vapor cleaning, such as contact angle measurement and atomic force microscopy (AFM) were carried out. Using XPS, the surface binding states of HF-vapor treated silicon surfaces were studied. Traces of fluorine and low oxygen coverage were monitored. An ozone treatment immediately after AHF cleaning increases significantly the fluorine concentration on the silicon surface. A beneficial impact of AHF and ozone on the electrical characteristics of 4 nm oxide films grown in oxygen by RTP in a cluster tool immediately after cleaning without breaking the vacuum was found.

Surface characterization of semiconductors with plasma and thermal waves analysis

The well characterized (100)-Si surface is used to demonstrate the capacity of the noncontact measurement of surface recombination velocity of excess carriers using photothermal heterodyne spectroscopy. The oxidized silicon surface is cleaned by an electron irradiation or by excimer laser in ultrahigh vacuum (UHV). The beam induced desorption and changes of surface binding states are monitored by Auger electron spectroscopy (AES). During the surface processing in UHV the sample is in situ excited by laser irradiation. The modulated reflectivity is recorded and change carrier and thermal wave analysis are carried out to measure the change of the surface recombination velocity. The influence of ion implantation and annealing on surface recombination velocity are monitored.

Theory of positronium formation on solid surfaces III. Thermal desorption of positronium from metal surfaces

Abstract We present a theory to describe thermal desorption of positronium from positron surface binding states using the resonant transition theory of positronium formation at solid surfaces. The results agree with experiments. The results affect the measurements of surface binding energy of positrons.

Theory of positronium formation on solid surfaces: III. Thermal desorption of positronium from metal surfaces

We present a theory to describe thermal desorption of positronium from positron surface binding states using the resonant transition theory of positronium formation at solid surfaces. The results agree with experiments. The results affect the measurements of surface binding energy of positrons.

Theory of positronium formation on solid surfaces: I. General theory and its application to positronium formation probability

We consider the micro-processes of positronium formation on surfaces with a new Hamiltonian, in which we treat the positron as a quantum particle. First we calculate the temperature dependence and the positronium work function dependence of the positronium formation probability in the case of no surface binding states. We succeeded in deriving a slightly increasing profile of the positronium fraction at low temperatures, as was found in the experiment of Lynn et al. We also calculated the probability of the positronium formation at excited levels and of the formation of the negative positronium ion. Furthermore, the positronium fraction is shown to be proportional to the length at which the surface electron density drops to half the maximum value.

Sputtering of ordered nickel-aluminium alloys: I. Introduction and preferential sputtering of Ni 3Al

A combination of several surface-sensitive microanalytical techniques have been applied to the study of selective or preferential sputtering by inert gas ion bombardment of aluminium from binary ordered nickel-aluminium alloys. Two discrete intermetallic compounds, Ni 3Al (this paper) and NiAl (the companion paper) have been examined in order to provide information regarding the contribution of surface binding states to sputter mechanisms. The use of atom-probe field-ion microscopy for analysis of ion-sputtered surfaces has permitted the depth of bombardment-induced composition profiles to be estimated and comparisons to be drawn between these depth profiles and those obtained by conventional surface analysis techniques. Studies of preferential sputtering in ordered structures have provided information through atom-probe analysis of fundamental and superlattice oriented specimens about composition profiles and bombardment-induced disordering processes. Consideration of these data have led to conclusions that two distinct “equilibria” may be involved in the formation of super-induced altered layers.