Papers by Keyword: Hillock

Abstract: The thermally generated defects will lower the life time in bulk silicon and cause increasing in the leakage current of individual diodes in integrated circuits, that will finally cause the malfunction with advanced devices and IC chips. The removal characteristics of hillock defects on the single bare silicon wafer generated by the thermal process were experimentally analysed with respect to the chemical additives enhanced uniform chemical etching and mechanical abrasion of high pure nano sphere colloidal silica interplaying with the alkali based polishing slurry. During the polishing, it was found that the silicon surface contacted with high speed of rotated polishing pad under the down force pressure is chemically dissolved by the slurry containing FA/O organic polyamine(R(NH2)n) agent with adding proper proportional FA/O I non ions surfactant, which effectively lowered the surface strain of slurry contacted to the reactive surface of the wafer and slurry enhanced uniform chemical etch leading to the hillock region and no hillock region. However, by the process of chemical mechanical polishing，the results show it can eliminate the hillock defects on the surface of silicon wafer thoroughly with high removal rate, and achieve lower surface roughness than before process of polishing.

Abstract: Stress migration behaviors in Tungsten (W) films were investigated according to morphological characteristics and residual stress analysis. Results show that stress relaxtion induced formation of voids and hillocks strips, which resembles the void / hillock pair observed in Cu film electromigration experiments. Analysis indicate that the formation of chocolate sphere shaped W hillocks is intimately related to the atoms diffusivity.

Abstract: The deformation process of sputtered tungsten films were investigated according to the morphological characteristics and residual stress analysis. Results show that there are four characteristics depending on the substrates and stress state. For thin films on polyimide, the localized plastic deformation is mediated by the alignment of grain boundaries in the case of tension or line bulges in the case of compression. It results from both in-plane and out-of-plane grain rotation. For thin films on silicon substrate, wedge cracks in the case of tension or regular hillocks in the case of compression become the typical morphology. From this point of view, the deformation behaviors of films depended on the substrate constraint and residual stress states.

Abstract: Annealing behavior of dilute Cu-X alloys (adding element X = transition metal and rare-earth metal with less than 3 at %) was investigated in terms of resistivity, internal stress, grain growth and hillock formation. The resistivity increases with addition of impurities regardless of kinds of adding elements. Generally, resistivity starts to decrease on annealing above 200 °C. Among present Cu dilute alloys, Sn addition shows the lowest resistivity 2.5 μΩcm on annealing at 400 °C. However, compared with a pure Cu film, salient grain growth of present dilute alloys does not takes place even at temperatures above 300 °C , where the grain size is nearly the same as that of as-deposited films. In-situ surface observation using an atomic force microscope (AFM ) revealed that hillocks did not grow on cooling stage (under tension), but started to form on heating stage (under compression). The scanning electron microscopy (SEM) observation of hillocks thus formed in present dilute alloy films shows that the external appearance of these defects was quite different from those observed in Al and Al alloy films. They most likely grow with a preferential crystal plane, not irregular growth like Al and Al alloy films. The internal stresses in most of the present as-deposited dilute Cu alloy films were nearly zero or compression of –25 to –100MPa, and upon annealing, they started to increase in tensile manner due to thermal stresses induced by the mismatch of the thermal expansion between substrates and deposited films. A large stress relaxation started to occur above 250°C, associating with a large number of hillock formation.

Abstract: Stress-assisted atomic migration occurs in thin films due to thermal stress development, followed by hillock and void formation on a film surface. Relation between thermal stresses and hillock formation was investigated on copper films with and without passivation layer. Copper films with a thickness of 10, 50 and 100 nm on oxidized silicon wafer were prepared for investigating thermal stress and hillock formation. In-situ thermal stress observation by X-ray measurement revealed that compressive stresses develop in an early stage of heating followed by a sudden decrease in the temperature region between 100 and 200 deg. In a cooling stage, stresses in a film linearly changed with decreasing temperature to form a tensile residual stress state. Surface morphology is observed by optical microscope and SEM after the heat cycle as well as at elevated temperatures in a vacuum chamber. Dome-like swells were formed on an AlN passivation layer. Almost of all of the swells on 100 nm thick film collapsed after the heat treatment up to 350 deg whereas the swells on 10 nm thick film had no collapse excepting a few case. Comparing with the film without passivation, the swell is considered to be the result of atomic migration of copper film to form hillocks in the interface between copper film and AlN passivation film during heating. Atoms are considered to migrate reversibly into the copper film in the cooling stage, resulting to make vacant hall in the swell of AlN film and then collapse due to tensile stress development.

Abstract: In-situ observation by scanning electron microscope of the microstructure evolution near the cathode depletion region and the quantitative analysis on the number of hillock phases in the eutectic SnPb edge drift structure made it clear that the dominant migrating element and dominant hillock phase were Sn and Pb, respectively, under 50 oC while both dominant migrating element and dominant hillock phase were Pb above 100 oC. Such temperature-dependence of the dominant hillock phases in the eutectic SnPb solder can be understood by considering the atomic size factors of the metallic solid solutions.