Chemical Mechanical Polishing of Germanium and Indium Phosphide for Microelectronic Applications

In recent times as the scaling down of the device dimensions is facing physical limits with currently used systems, new materials which have higher mobility like germanium (Ge) and III/V group compounds such as InP or InGaAs are being tested for future MOSFET devices. The integration of such materils into the current semiconductor fabrication processes requires, among other things, chemical mechanical planarization (CMP). Such a CMP process requires a slurry which can provide high removal rates (RRs) with low dissolution rates (DRs) while achieving good surface roughness values with minimal defects. Identifying such slurries is an important part of the thesis.;Since the formation of oxides of Ge can enhance Ge RRs, iodate based oxidizers (periodic acid, sodium periodate, potassium periodate, etc.) or hydrogen peroxide (H2O2) were added to a slurry containing silica particles to assist in the formation of the oxide. Among these, both high RRs and DRs were obtained in basic pH regions using H2O 2 silica based slurries. The high DRs will prevent achieving planarization. It is shown that these high rates are caused by the oxidation of Ge by hydroxyl radicals (*OH) and the rapid dissolution of the dissociation products of germanium hydroxides. There was no measurable dissolution near pH 2 where it was also possible to achieve RRs of ∼420 nm/min. The surface quality of polished wafer coupons, measured as root mean square (RMS) roughness using atomic force microscopy, was also very good, about ∼0.3 nm under these conditions. Thus this combination was used to polish patterned Ge wafer coupons.;In the second part, two dimensional (2D) profiles of Ge patterned wafers with a trench width of 160 nm obtained from atomic force microscopy (AFM) before and after polish, along with Ge and silicon dioxide (SiO 2) blanket wafer coupon RRs are reported. Also, dishing, surface roughness and oxide loss values of the coupons after polish are reported along with cross sectional scanning electron microscope (SEM) images. The minimum dishing value obtained for a single step CMP process was ∼15 nm with a roughness value of 0.3 nm. With a two step CMP process, better planarization was obtained with the desired recessed oxide layer but the roughness value of Ge surface was unacceptably high at about 0.7 nm.;The third part of the thesis deals with polishing of indium phosphide (InP) films. InP is used as a buffer layer between underlying silicon (Si) and indium gallium arsenide (InGaAs) films in which n-MOSFETs will be built. Results of the effect of abrasives, pH, slurry flow rate and oxidizer (H2O2) concentration on InP RRs are reported. The RRs were found to be higher for a larger total surface area of silica particles suggesting that silica particles have an affinity to InP. Contact area model was able to describe the removal of InP with silica particles. RRs with silica particles whose silanol groups have been replaced with methyl groups were lower than with unmodified particles, suggesting a possible bond formation between the silanol groups on the silica surface and InP during the polishing process. A removal mechanism is proposed based on these results.;The thesis is organized into seven chapters. The first chapter discusses the need for Ge and InP for future devices followed by an introduction to CMP. Chapter 2 reviews the existing published literature on Ge and InP CMP and chapter 3 lists the experimental techniques used. Chapter 4 discusses the initial results obtained while polishing a Ge disk and Ge wafers in the presence of various oxidizers along with the proposed Ge removal mechanism in the presence of each of them. In chapter 5, a detailed discussion on the CMP of Ge in the presence of H2O2 and silica particles is done. Chapter 6 presents the results of polishing of Ge STI structures with novel Ge CMP slurries. Finally, Chapter 7 provides a detailed analysis of InP CMP with silica particles.