Chien Chieh Lee

Silicon-based transmissive diffractive optical element

A silicon nitride (SiNx) membrane diffractive optical element (DOE) designed to exhibit beam-splitting and focusing behavior at visible wavelengths has been fabricated and tested. Since the fabrication process is based on silicon micromachining technology, the DOE is easily integrated with a laser diode chip and a photodiode chip on a silicon substrate to function as the hologram-laser-photodiode unit for use in the pickup head of a CD or DVD system. The SiNx film is deposited with low-pressure chemical-vapor deposition and the free-standing membrane is formed by KOH etching. The transmissive DOE showed a high diffraction efficiency (>20% for a binary-phase-level element). The experimental evaluation was in good agreement with the designed and modeled predictions.

Light extraction enhancement of InGaN MQW by reducing total internal reflection through surface plasmon effect

Coupling of a InGaN/GaN multi-quantum well (MQW) and semitransparent metal layer is shown to result in dramatic enhancement of spontaneous emission rate by the surface plasmon effect in the optical spectral range. A five-pairs 18.5nm InGaN/GaN MQW is positioned 175nm, form various thickness (t=5~50nm) silver layer. And periodic patterns (p=0.25~0.8μm) are defined in the top semitransparent metal layer by e-beam lithography, which are grating structures can be incorporated into the metal film to excite surface plasmon between the interference of the metal film and semiconductor. We have experimentally measured photoluminescence intensity and peak position of spontaneous emission of the fabricated structures and compared with the unprocessed samples, whilst still ensuring that most of the emission takes place into the surface plasmon (SP) mode. And the implication of these results for extracting light by reducing total internal reflection (TIR) from light emission diode is discussed.

Fabrication of Low-Stress SiN x H y Membranes Deposited by PECVD

SiN x films deposited on silicon in a plasma-enhanced chemical vapor deposition (PECVD) reactor from a mixture gas of SiH 4 and NH 3 are investigated as an alternative method for low-stress membrane fabrication. We verified that the stress in the silicon nitride films decreased as a function of deposition pressure. A low tensile stress in the film of 170 MPa was obtained at a pressure of 750 mTorr and the refractive index of the film was 1.8. After KOH wet etching from the back side of the silicon substrate, a flat square (5x5 mm) membrane with thickness of 500 nm could be successfully fabricated. The chemical composition of the film was analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, with lower deposition pressures producing less Si-H bonding.

Nanostructured diffractive optical elements on SiNX membrane for UV-visible regime applications

Silicon nitride (SiNX) film is a commonly used material in silicon technology. In addition, it has excellent optical properties. It is transparent in both the UV and visible range, with a high refractive index of about 1.7~2. Owing to its superior mechanical and optical properties, we used a silicon nitride membrane as an optical phase element. We will fabricate nano-structured diffractive optical elements, such as wave-plate, polarizer, and polarized beam splitter on SiNXHY membrane by e-beam lithography for the UV-visible regime applications. The SiNXHY membranes were made from SiNXHY films deposited by an plasma enhanced chemical vapor deposition (PECVD) as an alternative method for low stress membrane fabrication used in UV-visible transmittance. The stress of silicon nitride film showed a change from compressive to tensile with increasing working pressure during film deposition. The UV-visible transmittance of the free standing membrane was measured, which showed that UV light is transparent at wavelength as short as 240nm. We will show the feasibility to fabricate nano-structured diffractive optical elements on the SiNXHY membrane combined with microoptoelectromechanical systems (MOEMS) technology for the application in the UV-visible regimes.

Fabrication of optical transmission elements in an SiN x membrane

This paper presents a method for the fabrication of silicon-based optical elements in an SiNx membrane. This device will transmit visible and infrared light, and can be used for various types of optical elements, such as gratings, lenses, diffractive optical elements (DOEs), etc. This is a new designed structure for fabricating optical transmission elements. Since the fabrication processes are based on silicon micromachining technology, they can be easily incorporated with other active optical components in microoptoelectromechanical systems (MOEMS). An SiNx film is deposited by low-pressure chemical vapor deposition (LPCVD) and the free-standing membrane is formed by KOH silicon backside etching, from which substrate materials are removed. A transmission grating and Fresnel lens have been produced from this membrane. Scanning electron microscopic (SEM) images and the optical characteristics of the transmission grating are shown.

Fabry-Perot Type Antireflective Coatings for Binary Mask Applications in ArF and F 2 Excimer Laser Lithographies

We demonstrated an antireflective coating structure, which is based on a three-layer Fabry-Perot structure, for binary masks of ArF (193 nm) and F 2 (157 nm) excimer laser based lithographies. The antireflective coating structure is composed of a metal/dielectric/ metal stack. By adding different optimized structures, reflectance of less than 1% at both 193 and 157 nm have been achieved. At the Fabry-Perot structure, the bottom metal layer provides suitable absorption. By controlling the thickness of the intermediate dielectric layer, we can tune the minimum reflection regime to the desired exposure wavelength. The top metal layer can prevent charge accumulation during electron-beam writing.

Low Alkaline Contamination Bilayer Bottom Antireflective Coatings in F 2 Excimer Laser Lithography

A bilayer bottom antireflective coating (BARC) structure composed of tetraethoxysilane (TEOS) oxide and silicon nitride film stacks is demonstrated for F 2 excimer laser (157 nm) lithography. The top TEOS oxide film is anNH 3 contaminant-free material that can be used as an NH 3 capping layer. After an oxygen plasma treatment, the bilayer structure is shown to have high thermal stability by thermal desorption spectrometry. The measured swing effect is significantly reduced by adding the bilayer BARC structure. This BARC structure could also reduce the reflectance of various highly reflective substrates to less than 2% at 157 nm.

Si-based UV transparent subwavelength optical elements

The hydrogenated Silicon nitride film is well developed to form a passivation layer for non-volatile memory devices. It has many superior chemical, electrical, and mechanical properties. In addition, it also has excellent optical properties. It is transparent in UV and DUV range, with a high refractive index of about 1.7~2. Owing to its superior mechanical and optical properties, we used a hydrogenated silicon nitride (SiNXHY) membrane as an optical phase element. By using e-beam lithography, we demonstrate on feasibility for the fabrication of subwavelength optical elements, such as waveplate, polarizer, and polarized beam splitter on a silicon-based low stress SiNXHY membrane for the UV region applications. An SiNXHY film was deposited by plasma enhanced chemical vapor deposition (PECVD) and the free- standing membrane is formed by KOH silicon backside etching, from which substrate materials are removed. The membranes morphology and geometries of subwavelength optical elements were verified by means of an scanning electron microscope (SEM), and the optical performance characteristics of these subwavelength optical elements are shown. The experimental datas agree well with theoretical predictions.

Design and fabrication of Si-based pickup module for optical storage

We have proposed a miniaturized optical signal pickup module comprised of several SiNX membrane devices on stacked Si substrates for use in optical storage system. The optical module was designed to include not only light sources and detectors, but also the diffractive optical elements (DOEs), which can be made with microoptoelectromechanical systems (MOEMS) technology. Its optical operation was simulated by ray-tracing to have an optimized spot size (~0.6μm) focused on the disk with setting the tolerance of each element for the alignment. All these Si-based transmission optical elements were fabricated and can be stacked by self-alignment bonding for system assembly.

Realization of optical pickup head by using stacked silicon-based micro-optical system

We have developed a novel stacked silicon-based microoptical system, which is optical-on-axis and transmissible in both visible and infrared ranges. By using the new microoptical system techniques, we fabricated a miniaturized optical pickup head module. This optical pickup head consisted of a 650nm laser diode, a 45 degrees silicon reflector, a grating, a holographic optical element, and some aspherical Fresnel lenses. These optical phase elements fabricated on a SiNx membrane were free-standing on Si chips. Each element was then stacked by chip bonding. We could obtain a circular focusing spot on the optical disc as small as 3.1um.