Studies on a novel mask technique with high selectivity and aspect-ratio patterns for HgCdTe trenches ICP etching

A multiple mask technique, integrating patterned silicon dioxide (SiO2) film over patterned thick photoresist (PR) film, has been investigated as a method to perform mesa etching for device delineation and electrical isolation of mercury cadmium telluride (HgCdTe) third-generation infrared focal-plane arrays. The multiple mask technique was achieved by standard thick PR photolithography, SiO2 film deposition to cover the thick PR patterned film, and etching the SiO2 film at the bottom region after another photolithography process. The dynamic resistance in the zero-bias and low-reverse-bias regions of HgCdTe photodiode arrays isolated by inductively coupled plasma (ICP) etching with the multiple mask of patterned SiO2 and patterned thick PR film underneath was improved one- to twofold compared with a simple mask of patterned SiO2. It is suggested that the multiple mask technique is capable of maintaining high etching selectivity while reducing the side-wall processing-induced damage of ICP-etched HgCdTe trenches. The results show that the multiple mask technique is readily available and shows great promise for etching HgCdTe mesa arrays.

Commercial femtosecond micromachining system (FMS) has been developed that capable to process material in sub-micron (<200nm), micron and millimeter scale. The system structure and capabilities are presented. Basic functions of the system performance are controlled by sophisticated software. The files prepared with standard software can be acceptable for pattern fabrication. The results obtained by FMS are presented and discussed : bits in the range of 100-200 nm sizes, 6 TB/cm^3 density optical storage matrix, waveguides fabrication inside transparent materials, high aspect ratio (1 : 125) patterning of dielectric materials with Bessel beam, micro-drilling, micro-cutting and micro-pattern formation in the range of tens of millimeters.

LIGA is a well-established process to fabricate metallic micro parts with high resolution, high precision and very low sidewall roughness by means of X-ray lithography and electroplating. The availability of a precise X-ray mask is a precondition for the final precision of the manufactured micro parts. Typical mask substrate materials, e.g. beryllium, carbon based foils, Si3N4 or SiC show different disadvantages such as low X-ray transparency or high toxicity or high prices or low conductivity or high thermal expansion or surface porosity causing X-ray scattering. For the fabrication of X-ray masks, PMMA with its unique features such as high aspect ratio patterns with high precision, exhibits low sensitivity and the layers preparation is not easy. SU-8, an epoxy-based UV and X-ray sensitive, chemically amplified, negative tone photoresist exhibits high aspect ratio patterns with vertical sidewalls. The difficult remove of the resist after the electroplating process significantly hinders the inspection of the fabricated X-ray mask. We present the use and suitability of an UV sensitive, chemically amplified, viscous, aqueous-alkaline developable, and easy removable positive tone photoresist, XP mr-P 15 AV, exhibiting high aspect ratio patterns with vertical sidewalls for the fabrication of X-ray masks by means of UV lithography on vitreous carbon substrates.

Recently, there is a significant interest in using CA resists for electron beam (E-beam) mask making application. CA resists provide superior lithographic performance in comparison to traditional non CA E-beam resists in particular high contrast, resolution, and sensitivity. However, most current CA resists exhibit very large sensitivity to PAB and/or PEB temperatures resulting in significant impact on CD. In addition, image collapse issues associated with high aspect ratio patterning as well as electron scattering effects in low KeV tools necessitate thinner resists. Therefore, there is a need to have a high etch resistant resist system which can withstand the demanding chrome etch process. Previously, we reported on the KRS-XE resist which exhibits dry etch resistance comparable to the best deep UV resist and excellent lithographic performance and bake latitudes. No PEB is needed for this resist. In this paper, we report on an advanced KRS-XE resist formulation which exhibits dry etch resistance surpassing the industry standard, novolak, in the chrome etch process. This new resist also exhibits excellent lithographic performance - 50nm lines/space delineated and requires no PEB. This paper will highlight the lithographic and etch performance of this new resist.

We report on the electrical characteristics and the fabrication process of a nano-capacitor structure using metal-insulator-carbon nanotube-metal (MICNM) layers. The structure shows high capacitance and the possibility of ultra high integration density due to the unique nanotube structure. Nanoscale and high aspect ratio patterns are achieved by electron beam lithography for the fabrication of these vertical nanostructures. This structure can be applied to the substitution of capacitors employing the silicon pillar structure in dynamic random access memory (DRAM) or as a nanoscale capacitor for various nanoelectronic devices.

Step height removal mechanism of chemical mechanical planarization (CMP) for sub-nano-surface finish

Low energy protons in the several keV energy range have very limited penetration depths into polymer films. This limitation necessitates the use of very thin oxygen‐etch barrier layers and of dry image development by oxygen reactive ion etching. For negative tone images, the etch‐barrier layers were deposited patternwise by proton‐beam‐induced polymerizations of organo‐metallic compounds, followed with dry image development by oxygen reactive ion etching. For positive tone images, the etch‐barrier layers were deposited (prior to patternwise exposure to proton beams) on top of polymer films by plasma polymerizations of organo‐metallic compounds, or by evaporation or sputtering of certain metals. Hydrogen atoms and/or protons react with metal atoms in the etch barrier layers to yield volatile metal hydrides, making the exposed areas more vulnerable to oxygen reactive ion etching, and providing positive tone images after image development. Sub‐keV electrons can replace low energy protons for fabrications of positive‐tone polymer images. In these processes, almost any kind of carbonaceous polymer film can be used as the imaged material. With a bright ion gun available, the exposure times could be less than a second, yielding high aspect ratio and high resolution polymer patterns.

Topographically patterned surfaces are known to be powerful tools for influencing cellular functions. Here we demonstrate a method for fabricating high aspect ratio ( approximately 10) patterns of varying height by using two-photon polymerization process to study contact guidance of cells. Ridge patterns of various heights and widths were fabricated through single laser scanning steps by low numerical aperture optics, hence at much higher processing throughput. Fibroblast cells were seeded on parallel line patterns of different height ( approximately 1.5-microm, approximately 0.8-microm, and approximately 0.5-microm) and orthogonal mesh patterns ( approximately 8-microm and approximately 4-microm height, approximately 5-microm and approximately 5.5-microm height, approximately 5-microm and approximately 6-microm height). Cells experienced different strength of contact guidance depending on the ridge height. Our results demonstrate that a height threshold of nearly 1 microm influences cell alignment on both parallel line and orthogonal mesh patterns. This fabrication technique may find wide application in the design of single cell traps for controlling cell behavior in microdevices and investigating signal transduction as influenced by surface topology.

This thesis deals with the development of microfabrication technologies based on photoplastic structuring by lithographic and molding techniques. These technologies, combined with an original releasing method, allow for the simple fabrication of pseudo three-dimensional, soft, photoplastic microstructures with features and shapes that are difficult to obtain with standard micro-machining. The photoplastic material used is the SU-8 photoresist, a material that is used increasingly in the growing field of micro-electro-mechanical systems (MEMS). Photoplastic SU-8 microstructure fabrication is based on a combination of multi-layer spin-coating, molding and photolithographic processing of the resist on a prestructured silicon substrate. The final product is obtained by release of the structure from the substrate. This thesis describes several SU-8 microstructures which have been developed with an emphasis on atomic force microscopy (AFM) and scanning-near field optical microscopy (SNOM) probes. Scanning probe microscopy is a well-established technique for surface analysis, but batch-fabricated, low-cost probes still remain a challenging issue. Using a polymer for the cantilever facilitates the realization of mechanical properties that are difficult to achieve with classical silicon technology. The design, fabrication and testing of single lever and cassettes of multiple single-lever probes are presented and demonstrates the potential for fabrication structures with complicated shape and features. The fabrication process for SU-8 AFM probes is a simple batch process in which the integrated tips and the levers are defined in one photolithography step. Tip radii of curvature smaller than 15 nm have been obtained. The cantilever thickness depends on the spin-coating parameters, hence it can be very well controlled over a full wafer. Photoplastic cantilevers with thicknesses ranging from 1 to 6 μm have been produced. Imaging soft, condensed matter with photo-plastic levers, which uses laser beam deflection sensing, exhibits a resolution that compares well with that of commercially available silicon cantilevers. Lateral resolution of 5–6 nm has been estimated from imaging DNA-plasmid molecules. A vertical resolution of the order of 0.1 nm has been found. A similar fabrication technique was also developed to fabricate photo-plastic tips for SNOM that are to be attached to optical fibers. This technique allows optical apertures to be integrated at the end of the well-defined tip directly by probe fabrication, without the need for any post-processing for the aperture formation. Sub-100 nm aperture have been fabricated using this technique. Simple fabrication, as well as topographical and optical imaging demonstrate the potential of photoplastic-based probes for both AFM and SNOM applications, as well as for future combined probes development. In addition, the fabrication of functional microstructures by using SU-8 processing needs to be combined with other microfabrication techniques. Simple releasing of the molded structures from the substrate is especially of great importance. A sacrificial layer technique based on electrochemical etching enhancement has been developed and combined with the fabrication of the different photoplastic SU-8 probes presented. This technique allows the fast releasing of large microstructures and has been demonstrated by releasing other SU-8 photoplastic microfabricated devices.

Integration in the third dimension is becoming increasingly more common in advanced packaging to overcome limitations in Moore's Law. One popular example for 3D Integration is Package-on-Package (PoP), where memory stacks are mounted above the processor. This approach requires tall, high density Cu pillars for interconnection around the processor. Ever increasing I/O requirements creates a need for Cu pillars with smaller critical dimension (CD) in thick resist. This creates high aspect ratio challenges for materials and equipment. For lithography tools, low NA projection systems are fundamentally well-suited to achieve high aspect ratio patterns, due to the inverse relationship between depth-of-focus (DOF) and Numerical Aperture (NA). However, the NA of low NA steppers is not low enough for thick resists. The full-field projection scanner with lower NA provides superior performance than the stepper counterpart at higher throughput and lower cost. This paper presents the high aspect ratio performance of the full-field UV projection scanner tool in various thick resists ranging from 50um to 300um film thickness. Aspect ratios as high as 20:1 are demonstrated for square vias with 1:1 pitch. Further, as feature resolution is only practical with alignment, the alignment of thick resists is also included.

The authors present an empirical study of profile evolution of lithographically defined photoresist (PR) patterns during thermal reflow and apply the findings to diamond microlens fabrication. During PR reflow, a bulge forms at the edge of the PR pattern and propagates inwards as the temperature and PR thickness are increased. An empirical relationship for this propagation is derived. Furthermore, it was found that at a certain reflow temperature and a limited pattern size, there is a minimum initial thickness of the PR pattern for forming spherical lens profiles. Based on these findings, diamond microlenses with a diameter of 400 μm and a previously unachieved radius of curvature of over 13 mm were fabricated. This is underpinned by forming PR microlens patterns with a large radius of curvature and transferring the PR patterns through low-selectivity Ar/Cl2 inductively coupled plasma etching.

Laser interference lithography (LIL) is a technique that allows maskless patterning of large areal periodic nano/micro structures. The LIL pattern is often used as an etch barrier to pattern SiO2 intermediate layer in the fabrication process of high aspect ratio silicon nano/micro structures by deep reactive ion etching process (DRIE) with SiO2 etch barrier. In this study, a method to fabricate high aspect ratio nanograting structures by direct DRIE process of silicon substrate using LIL pattern without intermediate layer was developed as a simple and cost-effective fabrication process. To fabricate high aspect ratio silicon nanograting with high pattern fidelity, a simulation method to predict the cross sectional profile of photoresist (PR) pattern after exposure and development processes was investigated, and the LIL processing conditions were selected to obtain optimized cross sectional profile of PR pattern without residual layer based on the simulation results. To minimize the side wall defects during the DRIE process due to the deterioration of LIL pattern etch barrier, the processing conditions of DRIE process including etching gas, etching gas ratio, passivation time and power were optimized. Finally, a silicon nanograting with a grating pitch of 780 nm and height of 2.42 µm (aspect ratio: 6) was fabricated via the developed direct DRIE process with LIL pattern.

The transfer characteristics of the three-dimensional (3D) photoresist (PR) pattern to the aluminum titanium carbide (AlTiC) layer made for an air bearing surface (ABS) using the double-level lithography process and reactive ion etching (RIE) is investigated. The simulated process windows for single-level (conventional) and double-level lithography provide the process conditions to obtain desired PR thicknesses. The PR pattern with the underneath AlTiC layer is then etched with the designed recipe that consists of three consecutive etchings using CF4, O2, and CF4, respectively. The triple-step pattern is successfully formed on the AlTiC layer. The nonlinear relationship of the cumulative exposure and the PR thickness is believed to contribute to a decrease in etch selectivity of PR:AlTiC on the double-exposure area with the cumulative exposure.

This article shows the fabrication process and packaging of through polymer optical vias (TPOV). The TPOV enables encapsulation and packaging of silicon photonic systems using film assisted molding (FAM) and the creation of micron-sized through polymer optical vias. The optical vias are lithographically defined in thick film photoresist (~300 μm) and parallel processed on substrate level. Placing and connecting optical windows on individual chips using pick & place is a difficult and time-consuming process because of the stringent requirements on alignment accuracy, cost and throughput. In this work we provide a solution to this problem by combining microfabrication technology with backend film assisted molding technology for a new packaging approach for the integration of optical windows. As feasibility study we show through polymer optical windows on optical encoder Si photodiode arrays. The resulting microstructures are transparent in the spectrum of interest and hence serve as optical windows towards the substrate. Furthermore, our results show that the high aspect ratio (5:1) micro structure windows can be achieved and protected using FAMtechnology. The optical through package windows are accurately defined (±5 μm accuracy due to mask limitations) and can significantly improve the throughput. The total process time of a single wafer with up to 1260 chips and 20160 windows, including lamination, exposure and development, would approximately take 1-1.5 hours.

Photo-resist ashing by atmospheric pressure glow discharge