摘要:

Energy distributions (ED) of singly and doubly charged monatomic ion species (M+and M++) emitted from a Au–Si–Be liquid metal (LM) ion source were measured by using a sector magnet. The energy spreads of Si+and Si++decrease with an increase in the inclined emitter tip angle of 0°–20°. The drastic decrease in the Si+energy spread results from a disappearance of a shoulder on the low energy side accompanying the main peak in the profile. The reason for the disappearance of the shoulder may be that the energy deficit of field ionized ions decreases and merges in the main peak because of a weaker electric field strength on the off‐angle position. At the same time, a tail in the low energy region which is produced by charge transfer (CT) collision with doubly charged ions and neutral atoms also disappears with increasing the inclined angle, although the intensity of M++does not decrease seriously. This may be due to the difference in ion trajectories for both species caused by the difference in an initial velocity at the location where the CT collision takes place. Based on the drastic decrease in the energy spread, the figure of merit in the focused beam is also discussed.

ISSN:0734-211X    

DOI:10.1116/1.585695

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

When the liquid metal ion sources (LMIS) operate in the high‐current mode, an instability arises which is accompanied by ion current oscillations and microdroplets emission [Mair and Engel (1979), Sudraudetal. (1982, 1985)]. Two groups of microdroplets are observed differing in size, i.e., large ones (with radius of 2×102to 2×103Å) and small ones (with a radius of 10–100 Å). The intensity of small‐scale droplet formation proves to be two or three orders of magnitude higher than that of the large droplets [Thompson (1982)]. In this work it is shown that the appearance of the above groups of microdroplets is due to two instabilities developed in LMIS. The small droplets are due to the Rayleigh instability on the surface of thin cylindrical jets ejected from the tip of the Taylor cone at higher currents. This instability results in jet fragmentation and formation of small droplets (with sizes of the order of the jet radius) till the jet completely disappears.The recovery of the jets occurs within the time interval necessary for the most charged droplets to move towards the extractor as the screening effect of the droplets fades out and the electric field distribution on the cone surface is recovered. When the above time interval elapses the jet ejection reappears from the tip of the Taylor cone, and the jet fragmentation process is repeated. Thus, the Rayleigh instability is accompanied by the comparatively low‐frequency ion current oscillations which are due to the process of fragmentation and recovery of the jets (f≂107Hz). This process leads to liquid metal pressure modulation and causes the comparatively large‐scale capillary wave extension on the Taylor cone surface (wavelength ≂104Å) as a result of the Faraday parametrical effect. It is this effect that leads to formation of the large droplets generated on the Taylor cone surface. Emission of the small droplets occurs only in the cone axis direction, and that of the large droplets in a wider angular range.We have made measurements of the angular distributions of the large and small droplets, as well as of their intensities in the instability mode (I=120 μA,f≂10 MHz) in tin LMIS. The intensity of small droplet generation (with a radius of 15–100 Å) is approximately 1010–1011s−1and that of large droplet generation is two to three orders of magnitude less. The computed intensity values approached the ones observed. The small droplets are emitted mainly along the LMIS axis but as to the large ones, a wider spatial spread is observed. The measurements were carried out with transmission electron microscopy (TEM).

ISSN:0734-211X    

DOI:10.1116/1.585696

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The instability of solidification process occurring under the cooling of a metal melt is shown to be able to initiate short‐wave periodical structures on the surface provided the impurity concentration in the melt is sufficiently high. The experiments were carried out using titanium (plus yttrium) and copper (plus tin) targets melted by means of an ion beam. The mechanism of this phenomenon is associated with the solidification front instability caused by the constitutional supercooling of the liquid phase due to the impurities forced out into the latter under front motion. A dispersion equation for the solidification waves on the interphase boundary is derived for the thin melt case, its solutions are investigated as functions of the impurity concentration and heat transfer regime. The calculated values of the structure periods and excitation criteria are in good accordance with the experimental data. In our opinion, the short‐wave structures occurring on the solidified surface of liquid metal ion source [A. Wagner, T. Venkatesan, P. M. Petroff, and D. Barr, J. Vac. Sci. Technol.19, 1186 (1981)] may be caused by the above mentioned instability of the melt solidification process. In course of ion source operation, the impurities are produced by the cathode sputtering of the extractor [G. S. Galovich and A. Wagner, J. Vac. Sci. Technol. B6, 2108 (1988)].

ISSN:0734-211X    

DOI:10.1116/1.585697

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The emission current of a gallium liquid metal ion source (LMIS) was modulated at 500 KHz by focusing a modulated laser beam to 20 μm diam on the tip of LMIS. The peak‐to‐peak amplitude of the modulated ion current was 300 nA when the average laser power was 15 mW with 83% modulation depth, when the ion source was operated at 1–10‐μA dc emission current range. Total energy distributions of ions emitted by the LMIS were measured with and without modulation. We found minimal difference between the energy distributions spread with and without modulation, to within the experimental error.

ISSN:0734-211X    

DOI:10.1116/1.585698

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A helium field ion source emits intense beams from a (111) plane protruding from a tungsten emitter. Gomer’s hopping model was expanded to explain theI–Vcharacteristic of the plane. Our calculations agreed with the experimental results. To make a microprobe of helium ions, we constructed a 100 keV focusing column. It has a gimbal assembly and a phosphor screen with a microchannel plate to adjust the beam axis. Using a measured energy spread of 1 eV, the probe diameter was calculated to be less than 10 nm at a 1 pA probe current. Using scanning ion microscope images obtained with 90 keV helium ions, the actual probe diameter was estimated to be 2 μm. Although some improvements are necessary to focus the beam sharply, we showed the basic design of the focusing column for a helium field ion source.

ISSN:0734-211X    

DOI:10.1116/1.585699

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A method for calculating current density of a focusing system including the effects of finite source size, spherical, and chromatic aberrations is presented. Current density at the target plane can be determined by calculating the origin of trajectories at the object plane, for each target point. The relation between object and image points is calculated by numerical integration of the ray equation and using the analytical results from geometrical aberration theory. The focusing characteristics for current density distributions are also investigated. A focusing position which gives the maximum axial current density does not give a good beam current profile (measured by a knife edge) in the case of large aberrations, because the aberrations cause the current distribution to have a long tail.

ISSN:0734-211X    

DOI:10.1116/1.585700

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A study has been made to compare theoretical predictions of the performance of an optical column using a liquid metal ion source with experiment. Rather than estimating the beam size by calculating disks of confusion due to the chromatic and spherical aberrations, calculations of the current density profile were carried out using a new method which determines trajectories between object and image planes using the geometrical aberration theory. The trajectories are then used to find the current density which was then integrated to simulate the beam passing over a knife edge, so the rise distance could be estimated. It is shown that the focus conditions for optimum resolution of the beam may differ significantly from the conditions which optimize the rise distance of the beam. An experiment was then carried out to measure the actual rise distance for a variety of operating conditions of the actual ion gun. Good agreement was found between experiment and calculation.

ISSN:0734-211X    

DOI:10.1116/1.585701

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Emerging focused ion beam application (FIB) require that the incident ion range and lateral scattering be variable. It is desirable that the energy change required to alter the ion range produce a minimal variation of the incident beam diameter and current. A new FIB system with an energy range from 5 to 70 keV has been developed to meet these requirements. In order to produce a low energy fine ion beam with a high current density we have designed a column with two objective lens elements in tandem. The first element is a conventional einzel lens while the second is a retarding mode immersion lens. This immersion lens can also be operated as a short working distance einzel lens during high energy operation. In this paper the construction of the ion optical system and its performance are discussed. Initial results from ion induced secondary electron images demonstrates 100 nm resolution and a 20 nm resolution at 69 keV.

ISSN:0734-211X    

DOI:10.1116/1.585702

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The basic ideas of a systematic procedure for the automatic design of electron and ion optical columns with given focusing and deflection properties and minimum aberrations are outlined. The concept of synthesis is thoroughly explained. Optical columns can be synthesized either from given elements or in their entirety. The procedures are based on two different approaches: (1) Seeking the appropriate potential distributions in the form of spline functions with the subsequent reconstruction of the electrodes. (2) Using anapriorigiven multipurpose multielectrode system, the electrode potentials of which are selected so that the given constraints are satisfied and the aberrations are minimized. The first practical calculations show quite promising results.

ISSN:0734-211X    

DOI:10.1116/1.585659

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The resolution and alignment accuracy of FIB lithography is studied for making devices with 0.1 μm dimensions. 0.1‐μm linewidth patterns are successfully fabricated by 260‐keV Be++FIB for both positive and negative resists. 50‐nm linewidth Novolak based negative resist patterns are fabricated at 1.0×1012ions/cm2dose by 260‐keV Be++ FIB. Dot patterns with 0.3 μm diam and high density (108/cm2) are written on a 1×1 cm area in a PMMA resist to demonstrate that FIB lithography can be applied to make practical devices with a large writing area. Moreover, mark detection and overlay accuracy are studied for marks covered with PMMA and CMS resists. Finally, FIB lithography is applied to fabricate 0.1‐μm NMOS gate patterns. The overlay accuracy for hybrid exposure using FIB and an optical stepper is 0.2 μm at 2σ.

ISSN:0734-211X    

DOI:10.1116/1.585660

出版商:American Vacuum Society    

年代:1991

数据来源: AIP