In 3D packaging, Through Silicon Vias (TSVs) with high aspect ratios and depths measuring tens of microns are filled by advanced Cu electroplating processes. Today's 300mm TSV plating platforms are intended to produce bottom-up via fill, no seam voids, and minimal, controlled overburden. To achieve this, the preceding Cu-seed coverage must be continuous at a constant resistance, and the plating chemistries optimized. However, other factors such as hardware configurations and simple depletion of the plating formulations during the extended TSV process can lead to high Cu overburden thickness requiring a high removal rate (HRR) chemical-mechanical polish (CMP) process to remove the thick Cu layer.

Presented here are CMP results of a thick Cu overburden (~6um) resulting from the fill of 5 x 25um TSVs on 300mm wafers. The goal is to uniformly polish the overburden and utilize the tool's endpoint system at Cu clear before the next step of conventional barrier CMP. Slurries were screened for removal rate, uniformity, planarization ability, and defectivity. This study focuses on achieving a removal rate of >2.5um/min through evaluation of several commercial slurries in a multi-step polish application. Cross-sections post-plating show the Cu overburden, barrier and liner layer. Cross-sections post-CMP quantify Cu recess, dielectric loss, and presence/absence of seam defects. The process selected is demonstrated to achieve good planarization results with low occurrence of polish defects, at a rate and selectivity suitable for emerging 3D TSV Cu CMP applications.

In this study, the effect of the addition of electrolytes in a given ionic strength to various high-purity silica suspensions was investigated by measurement of the removal rates (RR's) in CMP processes on oxide layers under the same experimental conditions. As so-called slurries the following suspensions were used: i) silica sols produced by the Stöber process, ii) conventional silica sols based on alkali silicate as well as iii) suspensions of fumed silica, with the same SiO2 concentration in each suspension. Ionic strength of the added electrolyte was adjusted to e.g. 0.065 mol/l, with the electrolytes being HCl, NH4Cl, KOH, or binary mixtures of these substances.

These investigations revealed significant differences of the polishing behaviour between the different types of silica dispersions as slurries. While for the Stöber sols investigated, the RR's are highest in the acidic range and almost negligible in the alkaline pH range, fumed silica suspensions show an entirely different behaviour: RR is very low for acidic pH-values, and increases with the alkalinity of the slurry. In contrast to these observations, the RR's of slurries based on conventional silica sols are highest around the neutral point, and show a decrease for both more alkaline and acidic pH-values. In comparison to the other two types of material, these suspensions have a high amount of electrolyte background, originating from their manufacturing process.

A model is developed to explain these results in a comprehensive manner. It involves effects of the electrolyte type and the ionic strengths as well as influences of the particle size.

This work aims at attaining a more complete understanding of the principles governing resistive contrast imaging (RCI) of copper/low-k interconnects used for dielectric breakdown studies in a nanoprober scanning electron microscope (SEM) system. RCI is employed in such in situ dielectric breakdown studies to facilitate the localization of interconnect defect sites related to various stages in the degradation process of the low-k dielectric material. This work shows that RCI is suitable for detecting high-resistance sites, like opens, in copper/low-k interconnects. Moreover, RCI demonstrates potential in locating defects that lie deep in the test structure and are, thus, not detectable by SEM. A model is also proposed to explain the formation of RCI images of specific interconnect test structures with complex layout.

Chemical mechanical planarization (CMP) pads require conditioning to maintain the surfaces yielding optimal performance. However, conditioning not only regenerates the pad surface but also wears away the pad material and slurry transport grooves. Non-optimized conditioning may result in non-uniform pad profiles, limiting the productive lifetimes of pads. A new approach to conditioning uses closed-loop control (CLC) of conditioning sweep to enable uniform groove depth removal across the pad, throughout pad life. A sensor integrated into the conditioning arm enables the pad stack thickness to be monitored in situ and in real time. Feedback from the thickness sensor is used to modify pad conditioner dwell times across the pad surface, correcting for drifts in the pad profile that may arise as the pad and disk age. Pad profile CLC enables uniform reduction in groove depth with continued conditioning, providing longer consumables lifetimes and reduced operating costs.

This article reports on the characterization of two- and three-layer ohmic contacts comprising of titanium disilicide and nickel silicide. Cross Kelvin resistor test structures were used to extract the specific contact resistivity (SCR) values for the different ohmic contacts fabricated. The SCR of aluminum to titanium silicide (Al-TiSi2) ohmic contacts was evaluated to be as low as 6.0 x 10-10 Ωcm2. Three-layer ohmic contacts were created using aluminum and nickel silicide thin films and doped silicon. SCR values as low as 5.0 x 10-9 Ωcm2 to antimony-doped silicon and 3.5 x 10-9 Ωcm2 to boron-doped silicon were evaluated.

Critical dimension (CD) shrink and patterning of contact features via plasma etching were studied for typical resistive random access memory (RRAM) stacks. These consist of SiO2 and Si3N4 (total thickness of 65 80 nm) with NiO or pure Ni at the bottom. First, the contact patterning of RRAM stacks was investigated for 90 nm contacts. Thus, a standard high power contact etch recipe was shown to give rise to resist strip challenges due to the incorporation of sputtered Ni in the resist film. Therefore, a low-sputter-yield contact etch recipe based on a CF4/H2/Ar gas chemistry was introduced. The ion sputter efficiency of the recipe was estimated from a blanket SiO2 sputter-yield experiment in Ar plasma for the same recipe settings: this yielded values close to the Ni sputter-yield threshold. Second, plasma-assisted CD shrink was studied in combination with the newly developed patterning scheme to get the contact CD well below the initial 90-nm litho print size. It was shown that a low contact etch power regime could also provide a larger window for contact CD shrink using a C2H4-based chemistry: e.g. the demonstrated CD shrink from 90 nm down to sub-40 nm was shown to be extremely challenging in the case of a high power regime due to polymer instability enhanced with the resulting thickness increase. Perhaps, the relaxation of the polymer film stress, which was measured to be in the range of 1200-1500 MPa, is more easily triggered at higher power settings, which leads to polymer blistering. Finally, the optimization of the plasma-assisted CD shrink step in combination with the low-sputter-yield contact etch recipe was demonstrated to be able to provide CDs as small as 27 nm. The demonstrated approach shows that plasma-assisted CD shrink can provide a robust test vehicle for research programs that require the patterning of small features in the sub-40-nm CD range.