L. A. Nagahara

Effects of HF solution in the electroless deposition process on silicon surfaces

We have investigated the influence of HF concentration on the initial stages of electroless deposition for various metals (Al, Au, Cu, Sn, and Pd) onto silicon using atomic force microscopy. As the HF concentration in the plating solution increased, the rate of metal deposition correspondingly increased for Au, Cu, and Pd. In the case of Au and Cu, uniformly sized nuclei comprised the first deposited layer. However for Al and Sn, deposition occurred only at sporadic sites on the surface and was independent of HF concentration. For all of the metal ion studied, deposition initiated preferentially at flaws on the surface. The electroless process indicates a direct displacement mechanism which results in the simultaneous dissolution of Si as the metal ion is reduced at the surface. For all the metal ions deposited in this manner, metal adhesion to the Si surface was poor.

The influence of hydrofluoric acid concentration on electroless copper deposition onto silicon

Electroless metal plating is widely used in a variety of applications in the electronic and semiconductor industries such as selectively depositing on patterned substrates [1,2], making ohmic contacts [3-81, filling contact holes and vias in microelectronic devices [9,101, and delineating semiconductor junctions [ll-131. Some of the advantages of electroless deposition over conventional vacuum deposition techniques are its ease of use and low cost. Hence much research has gone into improving and utilizing this plating process. In contrast to the large number of papers dealing with electroless metal deposition on metal surfaces, relatively few papers have been written dealing with electroless metal deposition onto semiconductor surfaces, especially during the initial stages of formation. The advent of scanning probe microscopy, such as scanning tunneling microscopy WI&I) 1141 and atomic force microscopy (AFM) [15], enables the investigation of such processes to be performed simply on the nanometer scale. For example, Osaka and co-workers [16-181 have used STM to study the electroless plating process of magnetic materials (e.g. NiP and CoNiReP) on highly oriented pyrolytic graphite (HOPG). Moffatt Kennedy et al. [19] observed the growth of electroless copper films on Pd-activated HOPG and printed circuit boards. Phaner et al. [20] have reported STM observation of 100-200 nm thick electroless gold deposits on Pd-activated n-GaAs. In the case of electroless metal deposition onto Si, HF solution is occasionally used in the plating bath in place of a reducing agent in order to induce deposition onto the surface. The HF removes any residual oxide on the surface and more importantly aids in metal deposition through direct displacement of the silicon [9,21]. In this note, we

Strain imaging analysis of Si using Raman microscopy

We present two‐dimensional strain image mapping of the SiO2/Si interface on an Al/SiO2 patterned Si wafer using a modified Raman microscope. A positive shift in the Si Raman peak by approximately 1.0 cm−1, corresponding to 2.49×108 Pa compressive strain, was observed along particular edges between the Al/SiO2 patterned features and bare Si substrate. In addition to strain mapping, surface disorder in the Si wafer was also detected with this technique.

Mica etch pits as a height calibration source for atomic force microscopy

We describe a simple technique for creating etch pits in muscovite mica substrates for calibration purposes in atomic force microscopy (AFM). The etch pits are produced by wet etching the mica substrates in concentrated hydrofluoric acid and are formed with specific geometry. Along the long axis of the etch pits, steps of approximately 2 nm are observed which correspond to the molecular planes of mica. These steps bifurcate into 1 nm steps along the short axis. It is these 1‐ and 2‐nm‐high steps that permit height calibration.

In-situ observation of the electrochemical Hg/Au amalgam process on an Au electrode surface by atomic force microscopy

Abstract Atomic force microscopy (AFM) has been applied to investigate in situ the Hg/Au amalgam process by depositing the excess Hg atoms on an Au electrode surface in an acidic solution, which has led to form an Au/Hg alloy layer. We found that the formation of alloy layer proceeded through an island-growth mechanism and the growth of these islands is always fed by dissolution of nearby gold clusters. Based on AFM observations, a simple model of the Hg/Au amalgam process is proposed.

Thin semiconductor films: photoeffects and new applications

Abstract Current topics in photochemistry and photoelectrochemistry of thin semiconductor films are presented in regards to technological applications. Examples include photoelectrochemical reduction of CO 2 , photocatalytic applications for deodorization, metalization via photochemical reactions, and the photochromic behavior of MoO 3 .

Characterization of carbon material as a scanning tunneling microscopy tip for insitu electrochemical studies

We have studied the feasibility of using carbon as a scanning tunneling microscopy tip material for experiments conducted under electrochemical environments. The tips were found to be stable and durable in acidic or alkaline solution for several hours. The fabricated carbon tips were capable of resolving graphite atoms in electrolyte solution under potentiostatic condition as well as in air.

Observation and surface modification of electropolymerized poly(N‐methylpyrrole) using atomic force microscopy

We have used atomic force microscopy (AFM) to investigate the surface morphology of poly(N‐methylpyrrole) after electropolymerization on indium tin oxide and highly oriented pyrolytic graphite (HOPG) surfaces. We have found that the polymer surface became rougher with higher current density or lower solution temperature. In situ observations of the initial stages of electropolymerization revealed that an extremely weak adhesion exists between the polymer and HOPG. As a result, the AFM tip–sample interaction could easily move the polymer, and we have proposed that this can be used for patterning surfaces.

Scanning Probe Microscopic Investigation of Epitaxially Grown C60 Film on MoS2

C60 thin films have been fabricated on MoS2 surface by the molecular-beam epitaxy (MBE) and their monolayer coverages on this substrate have been investigated by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). STM study indicates that the C60 molecules pack either in a square lattice with lattice parameter of 11±1 A or a hexagonal close packed structure with lattice parameter of 10±1 A. The AFM images show column like structures similar to the square lattice pattern of STM images. Both STM and AFM techniques have been used to make a comparative study of C60 film grown on MoS2. The substrate lattice has also been imaged together with C60 molecular contours by STM in order to determine the epitaxial nature of the film.

In-situ atomic force microscope observation of stripping of mercury from HgAu alloy films in acidic media

We report the first in-situ atomic force microscope (AFM) observation of the stripping process of mercury occurring in HgAu alloy films. AFM images revealed that stripping preferentially occurred at the edges of defect sites during the initial stages and this process directly led the electrode surface to roughen with a multiple pit-like structure on nanometer scale. The formation mechanism of such structure is also discussed.