Jin-Jian Chen

Copper Deposition on HF Etched Silicon Surfaces: Morphological and Kinetic Studies

The kinetics and morphologies of Cu deposition on HF-treated silicon surfaces were investigated by atomic force microscopy (AFM), inductively coupled plasma mass spectroscopy (ICP/MS), and graphite furnace atomic absorption spectroscopy (GFAAS). The early stage (<60 s) of Cu deposition, as characterized by AFM, was found to be dominated by the nucleation of nanometer-sized Cu nuclei on HF-treated silicon surfaces. After 60 s of Cu deposition, the total grain number of Cu deposits was leveled to a constant plateau. However, a significant grain size increase of deposition Cu nuclei was noticed. We employed an AFM volume-integration technique in conjunction with the ICP/MS and GFAAS measurements to demonstrate that the Cu deposition rate was limited by the diffusion of Cu 2+ ions across the stationary solution layer toward the silicon surface.

Comparative Studies of Hydrogen Termination on Single-Crystal Silicon Surfaces by FT-IR and Contact-Angle Measurements

The hydrogen termination process on a Si(100) surface has been studied by multiple internal reflection infrared spectroscopy (MIR-IS) and contact-angle measurements. Three main silicon hydride absorption peaks at 2087, 2104, and 2114 cm−1 were found to gradually increase with the hydrofluoric (HF) acid etching. Eventually, a constant peak height was reached as an indication of complete hydrogen termination. Integration of all the surface hydrides absorption peaks (2000 to 2200 cm−1) provides direct quantitative evaluation of the hydrogen termination process. On the other hand, water contact-angle data were shown to consistently lag behind the IR measurement in determining the extent of hydrogen termination on the silicon surface. Analysis of the surface free energy of HF-etched silicon surfaces indicates that the degree of the hydrogen termination determined by water contact-angle measurements is subjected to inaccuracies due to the preferential hydrogen-bonding interaction between the water and silicon surface oxide.

Trace Level Organics in Hydrofluoric Acid Determined by Attenuated Total Internal Reflection Infrared Spectroscopy

Trace levels of organic impurities in the hydrofluoric acid solutions were measured by a multiple internal reflection infrared spectroscopic (MIRIS) technique. The MIRIS utilizes a clean attenuated total reflection (ATR) silicon crystal to extract organic impurities from the HF solutions. An open beam single-channel background spectrum combined with statistical analysis was used to ensure the reproducibility of absorbed organics measurement. The hydrofluoric acid samples were analyzed under an ultrapure nitrogen blanket to avoid airborne organics interferences. The adsorbed organic contaminants were found to randomly orient on the silicon ATR probe surface. A higher level of organic impurities was found in the more concentrated hydrofluoric acid solutions.

A New Potentiometric Sensor for the Detection of Trace Metallic Contaminants in Hydrofluoric Acid

Detection of ultratrace levels of metallic ion impurities in hydrofluoric acid solutions was demonstrated using a silicon-based sensing electrode. The sensors operation principle is based on direct measurements of the silicon open-circuit potential shift generated by the charge-transfer reaction between metallic ions and the silicon-based sensing surface. For instance, the silicon-based sensor is capable of detecting parts per-trillion to parts-per billion level of Ag + ions in HF solutions with a detection sensitivity of ca. +150 mV shift per decade change of [Ag + ]. The new sensor can have practical applications in the on-line monitoring of microelectronic chemical processing.

Ultrapure water quality monitoring by a silicon-based potentiometric sensor

A solid state silicon-based potentiometric sensor and a resistivity sensor were employed to monitor the water quality from an ultra-pure water production unit. A minute ionic impurity increase (at the low ppt level), which was not detectable by the conventional water resistivity sensor, can be sensitively detected by the silicon-based sensor. This slight degradation of water purity, independently confirmed by inductively coupled plasma mass spectrometry and atomic force microscopy, was attributed to early boil-off from the saturated water purification cartridge. The silicon-based sensor can potentially function as an ultra-sensitive monitoring sensor in conjunction with the conventional resistivity sensor to ensure water purity at parts per trillion level.

Monitoring metal ion contamination onset in hydrofluoric acid using silicon–diamond and dual silicon sensing electrode assembly

Potentiometric detection of trace levels of metallic contamination onset in hydrofluoric acid using a silicon-based sensor in conjunction with two non-contaminating reference electrode systems is presented in this paper. In the first case, conductive diamond was used as a non-contaminating reference electrode. Cyclic voltammetry and open-circuit potential experiments demonstrated the feasibility of using a conductive diamond film electrode as a quasi-reference electrode in the HF solution. In the second case, a dual silicon electrode system was used with one of the silicon-based electrodes protected with an anion permeable membrane behaving as the quasi-reference electrode. The dual silicon sensing electrode system possessed an additional operational advantage of being unaffected by the solution acidity. Though both sensing configurations were able to detect the metal ion contamination onsets at the parts-per-trillion to parts-per-billion levels, the dual silicon electrode design showed a greater compatibility for the on-line detection of metallic impurities in HF etching baths commonly used in semiconductor processing.

Study of fluoride induced dissimilar metal corrosion in a microelectromechanical system

This paper reports a study of microscopic on-chip corrosion on a 17 μ m × 17 μ m microelectromechanical device. The active atmospheric corrosion occurred only on the Al−Si−Ti components which were connected directly to the TiW components. Adsorbed fluoride ionic species on the microelectromechanical device were found to activate the observed bimetallic corrosion on the Al−Si−Ti/TiW contacts. Water rinse or replacement of TiW by TiAl x completely eliminates the active corrosion. Electrochemical potential data confirm the dissimilar metal corrosion mechanism. Effective prevention of on-chip corrosion was achieved by the judicious design of the device components to avoid dissimilar metal contacts with large galvanic potential differences.

Potentiometric Investigation of Silicon Electrode Immersed in Alkaline Hydrogen Peroxide Solution Containing Trace level of Iron

Sensing electrodes derived from the regular silicon wafer were shown to respond sensitively to the part-per-billion level of iron impurities in alkaline hydrogen peroxide solution (frequently referred to as standard clean-1 solution).The potentiometric results clearly indicate that the large positive shift of silicon open-circuit potential mainly originates from the adsorbed iron impurities on the surface oxide layer. Acid treatments by HCI or HF effectively regenerate the iron-contaminated silicon sensing electrode.