Electron Beam Lithography and Plasma Etching To Fabricate Supports for Studying Nanomaterials

Abstract—The fabrication processes of different nano- structures by electron beam lithography (EBL) and plasma dry etching are shown. The periodic circle and square patterns with different sizes were defined in the resist by EBL and then formed in the substrates by plasma etching. The holes were created with a diameter ranging from 1um to 5um and an etch depth from around 500nm to 1um. The quality and the size of fabricated patterns and their dependence on the etching time were investigated using top-down and cross-sectional scanning electron microscopy (SEM). It was found that the structures are well-resolved in the patterns with high levels of quality and good size uniformity. The results show that the depth of the structures does not depend on their size or geometry but rather on the etch time. Keywords: EBL,plasma etching,nano-structures.

Assessment of composition changes in demineralization and remineralization of human dentin using Raman spectroscopy/Beurteilung der Veränderungen in der Zusammensetzung von humanem Dentin durch Demineralisation und Remineralisation mittels Raman-Spektroskopie

To evaluate the whole process of demineralization and remineralization in human dentin using Raman spectroscopy (RS).Human molars from Chinese subjects were cut into tooth sections and painted with an acid-resistant varnish leaving one dentin surface exposed. The tooth sections were immersed in 0.3% citric acid to simulate the oral natural demineralization and were randomly divided into three groups with a sample size of n=12 each: 10 min (I), 20 min (II), and 40 min (III), according to the acid etch time. Then all the samples were submitted to a remineralizing solution for 5 days. The Raman spectra were measured before and after each treatment.The result showed that although there was no new constituent formed in the whole process, the peak intensities of inorganic constituents decreased with the increase of acid etch time, while the trend of the organic constituents were the opposite. After remineralization, the peak intensities of inorganic constituents increased again.In conclusion, using RS it would be possible to efficiently monitor the demineralization and remineralization status of human dentin.

Decapsulation Techniques for Cu Wire Bonding Package

This paper presents decapsulation solutions for devices bonded with Cu wire. By removing mold compound to a thin layer using a laser ablation tool, Cu wire bonded packages are decapsulated using wet chemical etching by controlling the etch time and temperature. Further, the paper investigates the possibilities of decapsulating Cu wire bonded devices using full wet chemical etches without the facilitation of laser ablation removing much of mold compound. Additional discussion on reliability concerns when evaluating Cu wirebond devices is addressed here. The lack of understanding of the reliability of Cu wire bonded packages creates a challenge to the FA engineer as they must develop techniques to help understanding the reliability issue associated with Cu wire bonding devices. More research and analysis are ongoing to develop appropriate analysis methods and techniques to support the Cu wire bonding device technology in the lab.

A Microelectronics-Compatible Process for Surface Micromachining of MEMS and MOEMS

Many fabrication steps for micro electromechanical and micro optoelectromechanical systems (MEMS and MOEMS) are carried out on specialized or highly customized tools that are not part of a standard microelectronics process flow. This paper presents a surface micromachining process for electrostatically-actuated MEMS devices using standard microelectronics tools, materials, and process conditions. The result should facilitate MEMS development in university laboratories with a microelectronics focus, and encourage the transfer of MEMS production to aging or underutilized industrial facilities. Aluminum structures, with silicon dioxide or silicon nitride dielectric layers, are built upon a silicon or glass wafer substrate. Shipley SC1827 photoresist provides a 2.7 μm thick sacrificial layer. The release etch is the critical fabrication step. This must be a dry process to avoid stiction, should be isotropic to minimize the etch time, and should be capable of large undercut distances to minimize the need for etch holes. Finally, the etch must be sufficiently selective to allow for the necessary release etch time without significantly impacting non-sacrificial structures. An O2/CHF3 plasma etch has been developed to meet these requirements. Using this process we have designed, fabricated and tested structures with moveable mirrors suspended over multiple drive and sense electrodes.

Studies on Chemical Methods to Expose Gate/Tunnel Oxide and Identification of Gate/Tunnel Oxide Defects in Wafer Fabrication

In failure analysis of wafer fabrication, currently, three different types of chemical methods including 6:6:1 (Acetic Acid/HNO3/HF), NaOH and Choline are used in removing polysilicon (poly) layer and exposing the gate/tunnel oxide underneath. However, usage is limited due to their disadvantages. For example, 6:6:1 is a relatively fast etchant, but it is difficult to control the etch time and keep the oxide layer intact. Also, while using NaOH to remove poly and expose the silicon oxide, the solution needs to be heated. It is also difficult to etch a poly layer with a WSix or a CoSix silicide using NaOH. In this paper, we will discuss these 3 etchants in terms of their advantages and disadvantages. We will then introduce a new poly etchant, called HB91. HB91 is useful for removing poly to expose the gate/tunnel oxide for identification of related defects. HB91 is actually a mixture of two chemicals namely nitric acid (HNO3) and buffer oxide etchant (BOE) in a 9:1 ratio. The experimental results show that it is highly selective in poly removal with respect to the gate/tunnel oxide and is a suitable poly etchant especially for removing polysilicon with/without WSix and CoSix in the large capacitor structure. Application results of this poly etchant (HB91) will be presented.

Failure Analysis of Discolored Bondpads in Wafer Fabrication

Discolored bondpads & non-stick failure in 0.6 μm wafer fab process with the hot Al alloy metallization was investigated. SEM, EDX & AES techniques were used to identify the root causes. Failure analysis results showed that discolored bondpads & non-stick failure were caused by TiN residue introduced during L95 bondpad opening wafer fab process. TiN residue on bondpad might have led to non-stick bondpad issue. The results also showed that it was difficult to determine the trace amount of TiN residue on bondpad using EDX technique due to its limitations. In this work, Auger surface analysis technique was used to determine TiN residue on bondpads with Al/TiW/Ti metallization. Auger results showed that Ti & N peaks were detected on discolored bondpads. It has resulted in non-stick bondpad failure. The solution to eliminate TiN residue on bondpads was to increase etch time at L95 bondpad opening wafer fab process. After using the new recipe with longer etch time, Auger results on the bondpads showed that no Ti & N peaks were detected and the bond-pull testing also passed.