Irradiation effects on solid surfaces by water cluster ion beams

The interaction between a water cluster ion beam and the surface of a silicon substrate was investigated. The sputtering yield of silicon by a water cluster ion beam was approximately ten times larger than that by an argon monomer ion beam. X-ray photoelectron spectroscopy was used to analyze the silicon surface irradiated with a water cluster ion beam. The analysis revealed that the surface was oxidized, and the oxidation was saturated approximately at the dose of 1 × 1014 ions/cm2. The number of disordered atoms measured by the Rutherford backscattering also supported the result

Surface irradiation and materials processing using polyatomic cluster ion beams

We developed a polyatomic cluster ion beam system for materials processing, and polyatomic clusters of materials such as alcohol and water were produced by an adiabatic expansion phenomenon. In this article, cluster formation is discussed using thermodynamics and fluid dynamics. To investigate the interactions of polyatomic cluster ions with solid surfaces, various kinds of substrates such as Si(100), SiO2, mica, polymethyl methacrylate, and metals were irradiated by ethanol, methanol, and water cluster ion beams. To be specific, chemical reactions between radicals of polyatomic molecules and surface Si atoms were investigated, and low-irradiation damage as well as high-rate sputtering was carried out on the Si(100) surfaces. Furthermore, materials processing methods including high-rate sputtering, surface modification, and micropatterning were demonstrated with ethanol and water cluster ion beams

Production and irradiation of ionic liquid cluster ions

We have developed a field-emission-type of cluster ion source using ionic liquids such as 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF_6). The current obtained was stable by placing a porous cap around the emitter. Time-of-flight (TOF) measurement showed that the peak mass number was approximately 5000 for positive and negative BMIM-PF_6 ion beams. This indicated that BMIM-PF_6 clusters with a size of a few tens of molecules were produced. With regard to the surface modification by BMIM-PF6ion beams, positive and negative cluster ion beams were used to irradiate Si(1 0 0) and glass substrates. Scanning electron microscope (SEM) and atomic force microscope (AFM) observations showed that the surface roughness of substrates increased. Furthermore, X-ray photoelectron spectroscopy (XPS) measurement showed that the composition ratio of layers deposited by positive or negative cluster ion beams was similar to that of BMIM-PF_6 solvent

Low-Damage and High-Rate Sputtering of Silicon Surfaces by Ethanol Cluster Ion Beam

To realize the high-rate and low-damage sputtering of a Si surface, the effect of irradiating an ethanol cluster ion beam on a Si surface was investigated. The sputtering depths in Si substrates induced by the ethanol cluster ion beam irradiation were larger than those in SiO2 substrates, which was due to a chemical sputtering effect. The lattice disorder and the surface roughness of the Si substrates decreased with increasing retarding voltage

Surface processing using water cluster ion beams

Vaporized water clusters were produced by an adiabatic expansion phenomenon, and various substrates such as Si(1 0 0), SiO_2, polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polycarbonate (PC) were irradiated by water cluster ion beams. The sputtered depth increased with increasing acceleration voltage, and the sputtering rate was much larger than that obtained using Ar monomer ion irradiation. The sputtering yield for PMMA was approximately 200 molecules per ion, at an acceleration voltage of 9 kV. X-ray photoelectron spectroscopy (XPS) measurements showed that high-rate sputtering for the PMMA surface can be ascribed to the surface erosion by the water cluster ion irradiation. Furthermore, the micropatterning was demonstrated on the PMMA substrate. Thus, the surface irradiation by water cluster ion beams exhibited a chemical reaction based on OH radicals, as well as excited hydrogen atoms, which resulted in a high sputtering rate and low irradiation damage of the substrate surfaces

Surface modification using ionic liquid ion beams

We developed an ionic liquid (IL) ion source using 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF[6) and produced IL ion beams by applying a hi]gh electric field between the tip and the extractor. Time-of-flight measurements showed that small cluster and fragment ions were contained in the positive and negative ion beams. The positive and negative cluster ions were deposited on Si(1 0 0) substrates. X-ray photoelectron spectroscopy measurements showed that the composition of the deposited layers was similar to that of an IL solvent. This suggests that a cation (A{+}) or an anion (B{−}) was attached to an IL cluster (AB)n, resulting in the formation of positive cluster ions (AB)nA{+} or negative cluster ions (AB)nB{−}, respectively. The surfaces of the IL layers deposited on Si(1 0 0) substrates were flat at an atomic level for positive and negative cluster ion irradiation. Moreover, the contact angles of the deposited layers were similar to that of the IL solvent. Thus, surface modification of Si(1 0 0) substrates was successfully demonstrated with BMIM-PF[6] cluster ion beams

Chemical erosion and sputtering of solid surfaces with liquid cluster ions

The sputtering phenomena of solid surfaces such as Si(111) and SiO2 surfaces were investigated using ethanol and water cluster ion beams. To be compared with Ar monomer ion irradiation, the sputtering yield of Si surfaces was approximately 100 times higher for ethanol cluster ion irradiation and approximately 10 times higher for water cluster ion irradiation. Furthermore, for the ethanol cluster ion irradiation, chemical erosion such as silicon hydride and hydro-carbide reaction occurred on the Si surface, which resulted in the high-rate sputtering of the surface. On the other hand, for the water cluster ion irradiation, oxidation occurred on the Si surface, and physical sputtering was performed on the surface. Based on these results, chemical reaction at a nano-scale area on the Si(111) surfaces was discussed from the thermodynamic approach, and the impact of cluster ions on the surface exhibited high temperature such as a few tens of thousands degrees, which resulted in the enhancement of the chemical reaction. Thus, liquid cluster ion irradiation exhibited unique erosion and sputtering even at room temperature, which were not obtained by a conventional wet process

Irradiation effect of gas-hydrate cluster ions on solid surfaces

In our newly developed gas-hydrate cluster ion source, a vapor of water bubbling with carbon dioxide (CO2) gas was ejected through a nozzle into a vacuum region, and mixed beams of water clusters and carbon dioxide-hydrate clusters were produced by adiabatic expansion. According to time-of-flight measurements, the largest water clusters consisted of approximately 2800 molecules at a vapor pressure of 0.3 MPa. Also, the largest mixed clusters contained approximately 2000 molecules. Copper and silicon substrates were irradiated by the water cluster ions as well as carbon dioxide-hydrate cluster ions. X-ray photoelectron spectroscopy measurements showed that carbon was included in the Cu and Si substrates irradiated by the carbon dioxide-hydrate cluster ions, and a chemical shift owing to the formation of carboxyl radicals occurred on the Cu surface. Furthermore, the Cu surface was sputtered, and the sputtering depth was larger than the distance penetrated by the water cluster ion irradiation. Therefore, the formation of carboxyl radicals played an important role in the sputtering of the Cu surface, which occurred effectively in carbon dioxide-hydrate cluster ion irradiation

Micro-patterning of Si(100) surfaces by ethanol cluster ion beams

The irradiation of Si(100) surfaces by ethanol cluster ion beams exhibited high-rate sputtering and low-damage formation. The sputtered depth increased with increase of the acceleration voltage for ethanol cluster ions, and the sputtering yield was a few hundreds times larger than that by Ar monomer ion beams. Also, the RBS channeling measurement showed that the irradiation damage was much less than that by Ar monomer ion irradiation. Furthermore, the AFM image showed that the surface roughness of the irradiated Si(100) surface was less than 1 nm. As well as the Si(100) surface, the sputtered depth of the photo-resist surface increased with increase of the acceleration voltage for ethanol cluster ions. Based on these results, micro-patterning with various sizes in a range of 3 μm to 100 μm was performed on the Si(100) surfaces by the ethanol cluster ion irradiation. Various kinds of photo-resist mask patterns such as circle, square and line patterns were made on a Si(100) surface by photo-resist technique. The SEM observation showed that micro-patterns were prepared on the Si (100) surface by the ethanol cluster ion irradiation

Interactions of fragment ions of tetradecane with solid surfaces

Vapors of tetradecane (C[14]H[30]) were ionized by electron bombardment. The generated fragment ions such as C[3]H[7], C[6]H[13], and C[12]H[25] ions were separated by an E × B filter (Wien filter) and accelerated toward Si(1 0 0) substrates. Thickness measurements showed that thin films were deposited on the Si substrates by C[3]H[7]- and C[6]H[13]-ion irradiation, although the Si substrate surface was predominantly sputtered by C[12]H[25] ions. Rutherford backscattering spectroscopy showed that the irradiation damage by the fragment-ion beams decreased with the increasing molecular weight of the fragment ions at the same acceleration voltage. Furthermore, Raman spectra as well as X-ray photoelectron spectroscopy measurements showed that DLC films were formed by C[3]H[7]- and C[6]H[13]-ion irradiation with the film thickness being larger in case of C[3]H[7]. On the contrary, for C[12]H[25]-ion irradiation, chemical sputtering occurred by surface reactions of hydrogen and methyl radicals with silicon atoms. The chemical reaction at the irradiated substrate surface could be enhanced by the higher temperatures achieved by the high energy–density irradiation effect of the polyatomic ions