C. Lehrer

Limitations of focused ion beam nanomachining

In this article, some limitations of the processing of structures with dimensions in the nanometer range by focused ion beams will be discussed. In order to enable exact depth control of nanometer structures, the effective sputter yield of silicon was determined as function of the ion dose. At ion doses below 1016 cm−2, the effective sputter yield is not constant and the volume of the area processed increases due to the implantation of ions. Material removal can be measured for doses above 2×1016 cm−2 and it reaches equilibrium for doses of about 3×1017 cm−2. This dose dependence of the effective sputter yield becomes especially effective in beam tail regions with low ion intensity. The shape of nanostructures is further determined by combining the beam shape and the angle dependence of the sputter yield which was experimentally determined. Using this approach with a Gaussian beam shape, a comparison of simulated and measured sidewall angles has shown good agreement for trench structures. Only sidewall regions close to the surface and to the bottom of deep structures show slight deviations. At the surface, non-Gaussian beam tails lead to unintentional sputtering at the corners of the processed area. At the bottom, forward scattered ions lead to higher sputter erosion.

Investigations on the topology of structures milled and etched by focused ion beams

For high precision micromachining of micro‐ and nanostructures by focused ion beams, the precision of the material removal process is of great importance. In this article, the topological properties of the ion beam generated structures like slope angles of trenches, surface roughness, and induced defects are investigated. The influence of the beam current and scanning strategy on the topological properties will be discussed. In addition, transmission electron microscopy analysis of thin lamellas generated by focused ion beams will be shown.

Tetramethoxysilane as a precursor for focused ion beam and electron beam assisted insulator (SiOx) deposition

Focused ion beams are intensively used for device modification by local material removal and ion beam induced metal deposition. With shrinking dimensions on modern multilayer devices, the need for ion beam induced insulator deposition is increasing. In this article, tetramethoxysilane as a precursor for ion beam induced deposition has been investigated. The influence of beam parameters dwell time and loop time on the material deposition rate will be discussed and compared to model calculations. For optimized scanning conditions, a maximum deposition rate of 0.33 μm3/nC was found. Insulating films were also deposited using an electron beam. The chemical composition and electrical properties of these films were compared with the films deposited by the ion beam. For electron beam deposition, the resistivity of the deposited films was 1×106 Ω cm which is two orders of magnitude higher than for ion beam deposited film.

UV nanoimprint materials: Surface energies, residual layers, and imprint quality

UV nanoimprint lithography is attracting more and more interest, because it has the potential of becoming a high-resolution, low-cost patterning technique. The availability of suitable UV curing materials is mandatory for successful imprinting. Within this work, a systematic investigation of commercially available photocuring materials was conducted to provide an overview of the properties of these materials. Their wetting behavior with respect to different substrate surfaces was characterized and their surface tensions were determined from their contact angles against two specifically selected solid surfaces: This method is presented here for the first time. The adhesion properties of the UV curing materials to different substrate surfaces and to the mold were investigated and necessary curing times were estimated. Additionally, the dependence of the residual layer thickness on the viscosity and the initial dispensed volume of UV curing materials was analyzed. It was found that the resist formulation of ...

Field emitter array fabricated using focused ion and electron beam induced reaction

A dual beam system consisting of focused ion and electron beams was used for manufacturing of Nb-gated silicon field emitter arrays. Gate opening was produced either by reactive focused ion beam etching of both the niobium and the silicon dioxide layer or by physical sputtering of the niobium layer by focused ion beam and subsequent wet etching of the underlying silicon dioxide layer. Platinum tips were deposited into the gate opening using an electron beam induced chemical reaction. Prototype devices, which exhibit field emission, were produced successfully. Several process parameters such as ion dose, beam diameter, and etch duration were systematically varied to identify the optimum condition for the fabrication of field emitter arrays.

Fabrication of field emitter array using focused ion and electron beam induced reaction

A 30 keV dual beam system with focused ion and electron beams has been used to develop a fast fabrication process of field emitter arrays (FEAs). The gate opening was fabricated by reactive focused ion beam etching. Pt cathode tips were deposited through gate opening using electron beam induced chemical reaction. Pt tips fabricated in the over-etched Si FEA showed field emission. A prototype of a nanometer-sized FEA was fabricated using a dual beam technique with FIB etching and electron beam induced deposition.

Defects and gallium-contamination during focused ion beam micro machining

Low energy focused ion beam (FIB) systems are used for the modification of integrated circuits, the preparation of TEM samples, the processing of structures in the sub -100 nm range, and for failure analysis. Focused gallium ion beams with diameters down to <10 nm (Full Width at Half Maximum) allow high resolution secondary electron surface inspection as well as local removal and deposition of material with high accuracy by physical sputtering or ion induced chemistry. Besides beam diameter and shape, gallium implantation and defect generation limit the application of FIB micro machining towards minimum resolution and sensitive analysis. Even when the desired structural dimensions are achieved, functionality of the sample may be hindered by implanted gallium and introduced defects. In this paper, vertical gallium distribution and lateral contamination for highly focused ion beam applications are investigated. SIMS analysis and Monte Carlo simulation are used for the determination for doses ranging from FIB inspection (1/spl middot/10/sup 14/ cm/sup -2/) to sputter removal at high doses (up to 1/spl middot/10/sup 18/ cm/sup -2/). The measurements revealed surface concentrations of 1/spl middot/10/sup 18/ cm/sup -3/ up to 6/spl middot/10/sup 21/ cm/sup -3/ and deep ranging tails. At doses exceeding 1.10/sup 17/ cm/sup -2/, the surface concentration reaches 6/spl middot/10/sup 21/ cm/sup -3/ and saturates, which is in agreement with simulations. Lateral contamination is determined by gallium background implantation due to inspection before processing and by non scanned neutrals. Defect generation was investigated by TEM. Even for typical FIB inspection at low doses (30 keV, 1/spl middot/10/sup 14/ cm/sup -2/) an amorphous layer is generated with a thickness of 50 nm.

Comparison of beam-induced deposition using ion microprobe

Abstract The localized Pt deposition on Si by 30 keV Ga + focused ion beam (FIB), 10 keV electron beam (EB) or dual beams (FIB and EB) using precursor gas has been compared by analysis using a 300 keV Be 2+ microprobe with a beam spot size of 80 nm. The distribution of deposited Pt, Ga from the ion beam itself, and C from the precursor gas was obtained at and nearby the deposited areas by micro-RBS spectra and RBS mapping. All of the beam processed areas showed a uniform Pt distribution at the deposited areas. The amount of Pt atoms increased with the increase in ion or electron dose due to the decomposition of precursor gas. The thickness of Pt layer by EB is considerably less than that by FIB due to the reduced deposition rate. Ga atoms from the center of processed areas partly redeposited at and nearby the FIB processed areas within ∼3 μm. The Ga incorporation by dual beam processing was reduced compared with that by FIB processing. The lateral distribution of low-Z elements such as C at and around the processed areas by about 10 μm is due to the adsorbed molecules of precursor gas during FIB processing.

In-line failure analysis on productive wafers with dual-beam SEM/FIB systems

Modern dual beam SEM/FIB tools will allow physical failure analysis on productive wafers in the cleanroom if contamination of wafer and production equipment can be controlled. In this study we show that the risks of Ga- diffusion and -desorption as well as heavy metal contamination can be overcome. The reentry of analyzed wafers into the production flow results in lower overall costs and a dramatically shortened feedback loop to production engineers, leading to reduced down times of production tools etc. Most FIB-applications (i.e. highlight etch of cross sections) can be processed with appropriate gas chemistry. Ion Beam deposition of an insulating material to refill the crater created by the sputtering process is also investigated. If either resolution is not sufficient or more complex analyses have to be applied a sample lift-out technique was developed making it obsolete to sacrifice wafers also in these cases. The fixed sample can be analyzed off-line with all PFA- methods, even plasma etching or lift-off in HF is possible. The benefits of this quantum leap for physical failure analysis are reduction of wafer costs and the possibility to reduce analysis cycle time as well as the number of learning cycles in technology development.

Microprobe Analysis Of Pt Films Deposited By Beam Induced Reaction

The localized Pt deposition by 30 keV Ga+ focused ion beam (FIB) or 10 keV electron beam (EB) induced reaction has been investigated using micro-RBS spectra and RBS mapping images by a 300 keV Be2+ microprobe with a beam spot size of 80 nm. The amount of Pt atoms increased with increasing ion dose due to the decomposition of precursor gas for FIB irradiation. Residual Ga atoms were found to be distributed at and near within 1.5 µm the deposited area due to the implantation from the Ga FIB and redeposition from the processed area, while low-Z elements such as C and O distributed at and around the processed areas by about 10 µm due to the adsorbed molecules of precursor gas after FIB processing. Micro-RBS spectra for EB induced deposited area show that the thickness of Pt layer is considerably less than that obtained by FIB due to the reduced deposition rate and the amount of Pt atoms at the boundary area was also less than that obtained by FIB, since the intensity profile of the electron beam was much shallower than that of FIB.