Ethanol Cluster Ion Beams Research Articles

Acetone cluster ion beam irradiation on solid surfaces

Acetone cluster ions were produced by the adiabatic expansion method without using a support gas. The acceleration voltage of the acetone cluster ion beam was from 3 to 9kV. The sputter depths of silicon irradiated with acetone cluster ion beams increased with acceleration voltage and fluence of the acetone cluster ion beams. The sputter depth was close to that induced by the ethanol cluster ion beam accelerated at the same acceleration voltage. The sputtering yield of silicon by the acetone cluster ion beam at an acceleration voltage of 9kV was approximately 100times larger than that for an argon monomer ion beam at 9keV. The sputter depths of silicon dioxide irradiated with the acetone cluster ion beams were smaller than those of silicon, but larger than those induced by ethanol cluster ion beams. The XPS analysis of silicon surface indicated that the silicon surface was more strongly oxidized by the irradiation of acetone cluster ion beam than ethanol cluster ion beam.

Surface irradiation and materials processing using polyatomic cluster ion beams

Abstract

Surface Interaction and Processing Using Polyatomic Cluster Ions

We developed two types of polyatomic cluster ion sources, one of which was a liquid cluster ion source using organic materials with a high-vapor pressure. Vapors of liquid material such as ethanol and water were ejected through a nozzle into a vacuum region, and liquid clusters were produced by an adiabatic expansion phenomenon. Another type was a cluster ion source using ionic liquids with a relatively low-vapor pressure. Positive and negative cluster ions were produced by a high-electric field emission. In addition, the interaction of polyatomic cluster ions with solid surfaces such as Si(100), SiO2, glass, and PMMA surfaces was investigated, and chemical sputtering was predominant for the Si(100) surfaces irradiated by ethanol cluster ion beams. Also, the irradiation damage of the Si(100) surfaces by ethanol and water cluster ion beams was smaller than that by Ar monomer ion irradiation at the same acceleration voltage. With regard to surface modification, PMMA surfaces were chemically modified by water cluster irradiation. Also, glass surfaces changed to electrically conductive surfaces by ionic liquid cluster ion irradiation. Furthermore, to demonstrate engineering applications of high-rate sputtering and low-damage irradiation by ethanol cluster ion beams, micro-patterning was performed on the Si surfaces.

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.

Chemical erosion and sputtering of solid surfaces with liquid cluster ions

The sputtering phenomena of solid surfaces such as Si(111) and SiO 2 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.

Characteristics of liquid cluster ion beam for surface treatment

A liquid cluster ion source, which is an ion source for the cluster beams produced with liquid materials, has been developed for the surface treatment of solid materials. The electrodes were designed for increasing the cluster beam intensity by a computer simulation of beam trajectories. The peaks of the cluster size distributions of the water and ethanol cluster ion beams of 3 atm vapor pressure were approximately at 2.4x10(3) and 1.6x10(3) molecules, respectively. The cluster size distributions of ethanol clusters were not sensitive to the variations of the acceleration voltages (V(e)) and currents (I(e)) of the electrons for ionization when the V(e) and I(e) were larger than approximately 200 V and 200 mA, respectively.

High-Rate Sputtering of Si and SiO<sub>2</sub> with Atomically Flat Surfaces by Using Ethanol Cluster Ion Beams

High-Rate Sputtering of Si and SiO<sub>2</sub> with Atomically Flat Surfaces by Using Ethanol Cluster Ion Beams

Size distribution measurement and separation of ethanol cluster ion beams

The distributions of the number of molecules per cluster (cluster size) of ethanol cluster ion beams were measured by the time-of-flight method. The cluster sizes at the peak and minimum tail (minimum size) of the distribution increased with increase of the retarding voltage. A difference appeared between the measured minimum size and the calculated values using a formula based on the early measurements on the velocity distributions of gas clusters.

Physical and chemical sputterings of solid surfaces irradiated by ethanol cluster ion beams

In order to clarify the interactions of ethanol cluster ion beams with solid surfaces, sputtering processes for Si, SiO(2) and Au surfaces were investigated by changing the acceleration voltage, the retarding voltage, and the incident angle. For the case of the normal incidence, the sputtered depth increased with increase of the acceleration voltage, and the sputtering ratio of Si to SiO(2) was approximately 10 at an acceleration voltage of 9 kV. Furthermore, with regard to the incident angle dependence, the sputtered depth for the Si surfaces had a maximum value at an incident angle between 10 degrees and 60 degrees . On the other hand, for the case of the physical sputtering by ethanol cluster ion irradiation on Au surfaces, the sputtered depth decreased with increase of the incident angle. With regard to the retarding voltage dependence, the sputtered depth had a maximum value for the Si surfaces, and the retarding voltage corresponding to the peak value changed according to the acceleration voltage applied. In addition, for the case of Au surfaces, the sputtered depth decreased with increase of the retarding voltage, and the physical sputtering was influenced by the minimum size of the cluster.

Irradiation effects of liquid cluster ion beams on silicon surfaces

We have developed a liquid cluster ion source, and produced liquid clusters such as ethanol and water clusters by an adiabatic expansion phenomenon. The average size was about 500 to 1000 molecules for the ethanol and about 2500 molecules for the water, respectively. The intensity of the cluster ion beams increased with increase of the vapor pressures. The irradiation effects of the liquid cluster ion beams on Si(100) surfaces were investigated. The sputtered depth increased with increase of an acceleration voltage for the ethanol and water cluster ions. In particular, the ethanol cluster ion irradiation sputtered the Si surface with the sputtering yield of approximately 100 times larger than that for Ar monomer ion irradiation. In addition, the Si surfaces after sputtering had an average roughness of less than 1 nm. Furthermore, the RBS channeling measurement showed that the irradiation damage of the Si surfaces by the ethanol and water cluster ions was smaller than that by the Ar monomer ion irradiation. This indicates that the low energy ion irradiation effect is predominant for the liquid cluster ion beams. As an engineering application of the liquid cluster ion beam process, the etching and patterning process were performed on the Si surfaces using metal masks. The mask patterns were formed very swiftly and finely by irradiation of the ethanol cluster ion beams.

Interactions of liquid cluster ion beams with metal surfaces

In order to investigate the interactions of ethanol and water cluster ion beams with metal surfaces, titanium (Ti) substrates were irradiated at different acceleration voltages. The sputtered depth increased with increase of the acceleration voltage. The sputtering yield of Ti at an acceleration voltage of 9kV for the ethanol cluster ions was approximately 100 times larger than that by argon (Ar) ion beams. On the other hand, for the case of the water cluster ion irradiation, the sputtering yield was a few tens times larger than that for Ar monomer ion irradiation. In addition, the AFM observation showed that the sputtered surfaces by the ethanol and water cluster ion beams had an average roughness of less than 1nm. For other metal surfaces such as Al, Ni, Cu, Ag and Au surfaces, the sputtering yield by the liquid cluster ion beams was also much larger than that by Ar monomer ion beams at the same acceleration voltage. Furthermore, the wettability of the Ti surfaces was changed drastically by the species of the cluster ions as well as the acceleration voltage. For the Ti surfaces irradiated by the ethanol cluster ion beams, the contact angle decreased with increase of the acceleration voltage, and it became about 10° at higher acceleration voltages. However, for the case of the water cluster ion irradiation, the contact angle was almost the same at various acceleration voltages, and it was about 80° which was larger than that of unirradiated surface.

Surface cleaning and modification of Si(100) substrates by ethanol and water cluster ion beams

The interactions of ethanol and water cluster ions with Si(100) substrates were investigated. The Si substrates were sputtered by the ethanol cluster ion beams, and the sputtering yield for the cluster ion irradiation at an acceleration voltage of 9kV was approximately 100 times larger than that for argon monomer ion irradiation at the same acceleration voltage. In addition, surface cleaning of the Si substrates, on which a small amount of metal vapors such as Cu, Al, and Au was deposited previously as contaminative particles, was performed by irradiation of the ethanol cluster ion beams. X-ray photoelectron spectroscopy measurements showed that the contaminative metal particles were removed from the Si surface at an ion dose of 1×1015ions∕cm2. Furthermore, contact angles as well as Fourier transform infrared spectra of the Si surfaces were measured, and the wettability of the surfaces changed drastically depending on the irradiation conditions of the ethanol and water cluster ions. This is ascribed to the difference in the chemical modification of the Si surfaces by the functional groups, which were produced after the impact of the ethanol and water cluster ions on the Si surfaces.

Interactions of ethanol cluster ion beams with silicon surfaces

The liquid cluster ion beam system was developed, in which cluster ions of organic molecules such as ethanol could be produced. In order to investigate the interactions of ethanol cluster ion beams with solid surfaces, SiO2 substrates and SiO2 films were irradiated at different acceleration voltages. The sputtered depth increased exponentially with the acceleration voltage. When the acceleration voltage was 9kV, the sputtered depths of Si and SiO2 at a dose of 1×1016ions/cm2 were 344.6nm and 47.2nm, respectively. The sputtering yield for the Si surface was approximately 100 times larger than that by Ar ion beams. With regards to the sputtering ratio of Si to SiO2, the ratio increased with decreasing acceleration voltage. This suggests that chemical reactions between Si and ethanol produced silicon hydride which was the dominant etching material for the Si surfaces.In addition, the AFM observation showed that the sputtered surface had an average roughness of less than 1nm. With regards to the crystalline state of the sputtered surface, the RBS and ellipsometry measurements were performed, and they showed that the Si surface damage induced by ethanol cluster ion irradiation was less than that by Ar monomer ion irradiation. Thus, Si surfaces etched at high sputtering speed by ethanol cluster ion beams had a lower damage and an atomically flat surface.

Fundamental characteristics of liquid cluster ion source for surface modification

We have developed a cluster ion source using liquid organic materials, which has several advantages for surface modification based on the different properties of liquid cluster ions. When vapors of liquid materials such as ethanol were ejected through a nozzle into a high-vacuum region, clusters were produced by an adiabatic expansion phenomenon. The clusters produced were ionized by an electron bombardment method, and the cluster ion current increased with increase of an electron current for ionization. In order to achieve the effective transport of cluster ion beams, a unipotential or einzel lens was used. The current density was much larger than that without using the lens. Furthermore, the beam diameter could be controlled by adjusting the lens voltage, and it was changed between 5mm and 20mm. In addition, several kinds of substrates such as Si, SiO2, PC substrates were irradiated at different acceleration voltages with ethanol cluster ion beams, and chemical and physical sputtering with a high sputtering yield was achieved. The sputtered surfaces were very smooth at an atomic level. The liquid cluster ion beams have a high potential for surface etching with the atomic level flatness, which is not obtained by a conventional wet process.