Eui-Goo Chang

Isothermal aging characteristics of Sn–Pb micro solder bumps

Abstract The shear strength of the under bump metallurgy (UBM) structure in both the high-melting solder bump and low-melting solder bump after aging were evaluated. Scanning electron microscopy and transmission electron microscopy were examined in the intermetallic compounds (IMCs) and bump joint profiles at the interface between solder and UBM. In 900 h aging experiments, the maximum shear strength of Sn–97wt.%Pb and Sn–37wt.%Pb decreased by 25% and 20%, respectively. The growth of Cu 6 Sn 5 and Cu 3 Sn was ascertained by the aging treatment. The crack path changes from the interior of a solder to the IMC interface. Compare with the Cu–Sn IMC, the amount of Ni–Sn IMC was small. The Ni layer is considered as the diffusion barrier.

Damage in etching of (Ba, Sr)TiO3 thin films using inductively coupled plasma

High dielectric (Ba, Sr)TiO3 thin films were etched in an inductively coupled plasma as a function of the Cl2/Ar gas mixing ratio. Under Cl2 (20)/Ar (80), the maximum etch rate of the BST film was 400 A/min and the selectivities of BST to Pt and PR obtained were 0.4 and 0.2, respectively. Etching by-products remained on the surface of BST and resulted in varying the stochiometry. Therefore, we investigated the surface of the etched BST using x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and x-ray diffraction (XRD). From the results of XPS analysis, we found that metal (Ba or Sr) chloride compounds remained on the surface of the etched BST for high boiling points. The morphology of the etched surface was evaluated with AFM. The surface roughness decreased as the Cl2 increased in the Cl2/Ar plasma. From the results of XRD analysis, the crystallinity of etched BST films under Ar only and under Cl2 (20)/Ar (80) was similar to that of as-deposited BST. However, the (100) diffraction pe...

Effects of BCl3 addition on Ar/Cl2 gas in inductively coupled plasmas for lead zirconate titanate etching

The lead zirconate titanate (PbZrxTi1−xO3:PZT) ferroelectric thin films have received great attention for the applications on nonvolatile memory, infrared sensor, electro-optical device, microelectromechanical system device, etc. In order to accomplish the integration of these devices, the etching process for both PZT film and electrode material must be developed. In this study, PZT etching was performed using planar inductively coupled Ar(20)/Cl2/BCl3 plasma. The etch rate of PZT film was 2450 A/min at Ar(20)/BCl3(80) gas mixing ratio and substrate temperature of 80 °C. X-ray photoelectron spectroscopy analysis for film composition was utilized. The chemical bond of PbO is broken by ion bombardment, and the peak of metal Pb in a Pb 4f peak begins to appear upon etching, decreasing Pb content faster than Zr and Ti. Also, the relative content of oxygen decreases rapidly. We thought that abundant B and BCl radicals made a volatile oxycompound such as BxOy and/or BCl–O bond. To understand the etching mechani...

Optimization of post-CMP cleaning process for elimination of CMP slurry-induced metallic contaminations

We have invetigated the slurry-induced metallic contaminations of undoped and doped silicate oxide surface during the post-chemical mechanical polishing (CMP) cleaning process. The metallic contaminations by CMP slurry were evaluated in the four different oxide films, such as plasma enhanced tetra-ethyl-ortho-silicate glass (PE-TEOS), O3-boro-phospho-silicate glass (O3-BPSG), PE-BPSG, and phospho-silicate glass (PSG). Prior to entering the post-CMP cleaner, all films were polished with KOH-based slurry. The total X-ray fluorescence (TXRF) measurements showed that all oxide surfaces are heavily contaminated by potassium and calcium during polishing, which is due to the CMP slurry. The polished O3 BPSG films presented higher potassium and calcium contaminations compared to PE-TEOS film because of a mobile ion gettering ability of phosphorus. For PSG oxides, the slurry-induced mobile ion contamination increased with an increase of phosphorus content. In addition, the polishing removal rate of PSG oxides had a linear relationship with phosphorus content.

Study on surface reaction of (Ba, Sr)TiO3 thin films by high density plasma etching

Ferroelectric devices are extremely useful for dynamic random access memories applications because of their high dielectric constant. Using ferroelectric device structure, manufacturing cell capacitance of highly integrated memory device is possible. The small feature size requires anisotropic etching. Since the research of (Ba, Sr)TiO3 thin film etching is seriously lacking, we studied the surface reaction of (Ba, Sr)TiO3 thin films by using high density plasma etching. In this study, (Ba, Sr)TiO3 thin films were etched with Cl2/Ar gas combination in an inductively coupled plasma. This was done by varying the etching parameters such as radio frequency power, direct current bias, and chamber pressure. The maximum etch rate of the BST films was 560 A/min under Cl2/(Cl2+Ar) of 0.2, 600 W/250 V, and 5 mTorr. The selectivity of BST to Pt and SiO2 was 0.52, 0.43, respectively. The surface reaction of the etched (Ba, Sr)TiO3 thin films was investigated with x-ray photoelectron spectroscopy (XPS) using narrow sc...

Removal characteristics of hillock on SnO2 thin film by chemical mechanical polishing process

SnO2 is one of the most suitable materials for gas sensors. The microstructure and surface morphology of SnO2 films must be controlled because the electrical and optical properties of SnO2 films depend on these characteristics. We investigated the effects of chemical mechanical polishing (CMP) on the variation of morphology of SnO2 films prepared by rf sputtering system. The commercially developed ceria-based oxide slurry, silica-based oxide slurry, and alumina-based tungsten slurry were used as CMP slurry. Nonuniformities of all slurries coincided with stability standards of less than 5%. Silica slurry had the highest removal rate among three different slurries. In addition, the particle size analysis showed that silica slurry had an abrasive with the largest average particle size of the three. Based on the atomic force microscopy analysis of thin film topographies and root mean square values, silica slurry has excellent properties that allow the application of SnO2 thin films as gas sensor materials.

Effects of phosphoric acid stabilizer on copper and tantalum nitride CMP

Abstract The effects of phosphoric acid addition on slurry for chemical–mechanical planarization (CMP) of copper and tantalum nitride were investigated. It is generally known that the slurry for copper CMP consists of alumina or colloidal silica as an abrasive, organic acid as a complexing agent, an oxidizing agent, a film forming agent, a pH control agent and additives. Hydrogen peroxide (H2O2) is one of the materials that are commonly used as an oxidizing agent in copper CMP. However, hydrogen peroxide needs some stabilizers to prevent decomposition. We evaluated phosphoric acid (H3PO4) as an accelerator of the tantalum nitride CMP as well as process a stabilizer of the hydrogen peroxide. We also estimated dispersion stability and zeta potential of the abrasive slurry with the contents of phosphoric acid. An acceleration of the tantalum nitride CMP was verified through the electrochemical test. This approach may be useful for the development of the second step copper CMP slurry or in general stabilization of hydrogen peroxide in abrasive slurry.

Chemical mechanical planarization characteristics of WO3 thin film for gas sensing

It is important to control the microstructure and surface of films to use them in gas sensors. Chemical mechanical polishing (CMP) processing is one of the most useful methods for improving the surface roughness of films. The effects of CMP on the surface morphology of WO3 thin films prepared by the rf sputtering system were investigated in this article. The removal rate of the films increased, and the rms surface roughness decreased with the addition of an oxidizer to the tungsten slurry. Within-wafer nonuniformity was improved to below 5% when oxidizers of 5.0 and 2.5vol%, respectively, were added to the tungsten slurry. The optimized oxidizer concentration, reflected by both the rms roughness values and a hillock-free surface with the good uniformity, was 5.0vol% as shown with atomic force microscopy analysis of thin film topographies. Our CMP results will be a useful reference for advanced technology of thin films for gas sensor applications in the near future.

Etching characteristics of SrBi2Ta2O9 film with Ar/CHF3 plasma

Among the ferroelectric thin films that have been widely investigated for ferroelectric random access memory (FRAM) applications, the SrBi2Ta2O9 (SBT) thin film is appropriate as a memory capacitor material due to its excellent fatigue endurance. However, very few studies on the etch properties of SBT thin films have been reported, even though dry etching is an area that demands a great deal of attention in the very-large-scale integration of ferroelectric thin-film capacitors for FRAM applications. In this study, SrBi2Ta2O9 thin films were etched using a magnetically enhanced inductively coupled Ar/CHF3 plasma. Etch properties, such as etch rate, selectivity, and profile, were measured for different gas mixing ratios of CHF3/(Ar+CHF3), while the other process conditions were fixed at rf power of 600 W, dc-bias voltage of −150 V, and chamber pressure of 5 mTorr. The maximum etch rate of SBT thin films was 1650 A/min under CHF3/(Ar+CHF3) of 0.1. Selectivities of SBT to Pt and photoresist masks were 1.35 an...

Electrochemical Patterning of Copper Using Microcontact Printing

This paper demonstrates that micropatterns of copper films can be fabricated by selective electrochemical etching of copper using microcontact printing of self-assembled monolayers (SAMs). The elastomeric stamps which have microstructures on their surfaces are made out of polydimethylsiloxane and then are inked with a solution of an alkanethiol in ethanol. SAMs of alkanethiol are patterned on the copper films by contacting stamps with the substrates. The patterned substrates are etched electrochemically in an electrolyte. SAMs of alkanethiol act as an electrochemical barrier leading to selective etching of copper films. Microstructures of copper with dimensions as small as 1.5 μm have been produced using this procedure. This method shows the capability of fabricating simple structures on a scale comparable to UV photolithography which produces printed circuits of copper for the semiconductor industry.