Yongqi Fu

Semiconductor microlenses fabricated by one-step focused ion beam direct writing

We fabricated a refractive semiconductor micro-lenses using a focused ion beam (FIB) direct writing technique. The simple one-step FIB process produced high-quality micro-lenses of silicon, the most popular and low cost semiconductor material used in optoelectronics. A spherical Si microlens with a nominal lens diameter of 48 /spl mu/m exhibited a radius curvature and focal length of 100 and 40 /spl mu/m, respectively. The maximum derivation between the measured and designed profiles is less than /spl lambda//100. The surface roughness, RMS, measured by use of atomic force microscope in 1/spl times/ 1 /spl mu/m/sup 2/ square area, is 1.1 nm. This microlens fabrication method could be readily applicable due to the simplicity in processing and the high-quality results.

Influence analysis of dwell time on focused ion beam micromachining in silicon

Influence of dwell time on focused ion beam (FIB) micromachining process by means of single pixel writing mode sputtering silicon is discussed in this paper. It affects line broadening and sputtering depth during the milling process in silicon material. It is proved by the experimental results that long dwell time leads to deep milling depth due to reducing scanning numbers of pixel. The broadening effect by the wing of Gaussian distribution profile is different from the variation of beam limiting aperture size. In the case of the aperture size 150 μm and below, the effect is little with changing of dwell time. It is obviously serious for large aperture size with the short dwell times of less than 3 μs.

Characterization of focused ion beam induced deposition process and parameters calibration

Deposition of metal or insulator by focused ion beam (FIB) technology is very useful for microsensor fabrication, IC chip modification and failure analysis. Characteristics of depositing tungsten is studied, and physical model is put forth in this paper. The deposition quality of the deposited layer was analyzed by varying operating parameters, such as dwell time, beam spot size, beam current and refresh time. By analyzing the experimental results, optimum parameters are derived for deposition process so as to provide experimental basis for actual application in the future. It is verified by the results that the physical model is in accordance with actual operation condition.

Investigation of microlens mold fabricated by focused ion beam technology

Abstract A novel fabrication method of microlens mold, focused ion beam (FIB) milling, is presented in this paper. Substrates with different materials, copper, nickel, and bulk silicon, were used in order to compare their milling quality. Two-dimensional profiles and surface roughness of the fabricated molds were measured using a laser interferometer. Finally, the mold was used for hot embossing replication. The surface roughness ( R a value) of the replica is about 8 nm, and the profile is neat and symmetric. Measured sizes of the replica coincide well with that of the design.

Hybrid microdiffractive-microrefractive lens with a continuous relief fabricated by use of focused-ion-beam milling for single-mode fiber coupling.

The design, microfabrication, and testing of a hybrid microdiffractive-microrefractive lens with a continuous relief that is used with a laser diode for monomode fiber coupling is discussed. The hybrid microlens with a diameter as small as 65 mum and a numerical aperture of 0.25 is fabricated directly onto a spherical surface by use of focused-ion-beam milling technology. A focused Ga(+) ion beam is used to mill the continuous relief microstructure at an acceleration voltage of 50 kV. From the test results a coupling efficiency of 71% (-1.49 dB) was achieved at room temperature. A diffraction efficiency of the main diffractive order, -1, was measured to as high as 90.5% at a wavelength of 635 nm. This indicates that the hybrid microlens was suitably designed within the application requirements and satisfactorily manufactured with focused-ion-beam milling.

A novel one step integration of edge-emitting laser diode with micro-elliptical lens using focused ion beam direct deposition

An edge-emitting laser diode (LD) integrated with a microlens on its emitting surface for the purpose of collimating and fiber coupling is introduced in detail in this paper. A micro-elliptical lens is adopted for the integration in terms of divergence angle in both parallel and transverse directions. The lens with dimensions of 50 /spl mu/m/spl times/30 /spl mu/m/spl times/4 /spl mu/m is microfabricated on the emitting surface of the laser diode with operating wavelength of 635 nm directly by focused ion beam (FIB) deposition function. The SiO/sub 2/ deposition is realized by programming of the FIB machine. It is shown by test results that the focused spot size in the parallel and transverse propagation directions are 7.9 and 9.1 /spl mu/m (at site of 1/e/sup 2/), respectively, and the coupling efficiency of the compact and miniaturized system can reach as high as 71%. Measured far-field angles (full angle) with the microlens in both parallel and transverse directions are 2.2/spl deg/ and 1.2/spl deg/, respectively. Compared with the original divergence angles of 31/spl deg/ and 14/spl deg/ without the micro-elliptical lens, they were greatly reduced by this method.

Microfabrication of diffractive optical element with continuous relief by focused ion beam

The diffractive optical element (DOES) with continuous relief and submicron feature size is very useful for optical fibre communication due to its perfect coupling. Microfabrication of the DOES by focused ion beam (FIB) technology is introduced in detail in this paper. Based on analyzing influencing factors such as ion dose, beam spot size, beam current and dwell time etc., controlling the process of continuous relief form is discussed. It is shown by testing results that the form of milled continuous relief is accurate enough for the application of fibre communication with its high diffraction efficiency.

Investigation of integrated diffractive/refractive microlens microfabricated by focused ion beam

Integrated diffractive/refractive microlens with dual focus point is introduced in detail in the view of design, microfabrication, and testing. Two manufacturing methods—milling and deposition directly by focused ion beam technology is discussed and compared. It was shown by testing results that the deposition method is more suitable to form the refractive spherical/aspherical lens and milling is suitable for microfabrication of diffractive optical elements. Focusing spot size (full width at half maximum) are 0.55 and 0.87 μm (λ=638 nm) for refractive and diffractive lens, respectively, with NA 0.35 and 0.5.

Calibration of etching uniformity for large aperture multilevel diffractive optical element by ion beam etching

Ion beam milling is a suitable technique for manufacturing optical elements. It has the advantages of accurately controlling and maintaining a constant optical index. However, it is very difficult to ensure etching uniformity on large areas due to the instability of the machine during sputtering. In this article, the etching speed is analyzed, and selection criteria of corresponding technological parameters are proposed. An available calibration method is put forth to improve etching depth uniformity. Etching is divided into several steps and the sample is rotated to change its position on the target after each step. It is proved by experiment that this is very practical for actual fabrication with a 5%–15% improvement of depth uniformity from previous results.Ion beam milling is a suitable technique for manufacturing optical elements. It has the advantages of accurately controlling and maintaining a constant optical index. However, it is very difficult to ensure etching uniformity on large areas due to the instability of the machine during sputtering. In this article, the etching speed is analyzed, and selection criteria of corresponding technological parameters are proposed. An available calibration method is put forth to improve etching depth uniformity. Etching is divided into several steps and the sample is rotated to change its position on the target after each step. It is proved by experiment that this is very practical for actual fabrication with a 5%–15% improvement of depth uniformity from previous results.