Heather Claire Galloway

The influence of chemical treatments on tungsten films found in integrated circuits

Abstract The influence of four different chemical solutions on the composition, morphology, and etch rates of thin, chemically vapor deposited tungsten films have been investigated. These films are the standard material patterned to create tungsten plugs in integrated circuits through a chemical mechanical planarization (CMP) step. The tungsten films were treated with aqueous solutions of KOH, KIO 3 + NaOH , H 2 O 2 + NH 4 OH , and H 2 O 2 +HCl. We have evaluated the resulting changes in the surface chemical composition of the tungsten film with X-ray photoelectron spectroscopy (XPS). Changes in film morphology have been recorded with atomic force microscopy and material removal rates have been determined with calibrated four-point-probe resistivity measurements. Together, these measurements demonstrate the complex manner in which chemical pre-treatments in the CMP process influence thin tungsten films.

Microscopic Studies of Friction and Wear at the Benzotriazole/Copper Interface

Interfacial friction and topographic changes at copper surfaces have been measured in situ with AFM in nitric acid and in acidic and neutral solutions of benzotriazole (BTA), a known corrosion inhibitor. In addition, changes in the thickness of the copper film have been measured ex situ using stylus profilometry as a function of solution treatment. These measurements demonstrate isotropic dissolution in 0.10 M HNO3 solutions and little change in neutral solutions of BTA. However in acidified solutions of BTA, the formation of a substantial reaction overlayer, the presence of higher interfacial friction, and the tip-mediated, localized dissolution of copper interface is observed. These measurements indicate that BTA plays a multifunctional role under acidic conditions. In the absence of mechanical action, BTA acts to passivate the surface from isotropic etching under acidic conditions. In regions of interfacial contact, the dissolution of a BTA-Cu reaction layer leads to the localized removal of copper through a tip-mediated process.

pH-mediated frictional forces at tungsten surfaces in aqueous environments

We have used atomic-force microscopy to measure the change in interfacial friction and adhesion between a tungsten surface and bare or alumina-coated Si3N4 tips. These measurements have been made in aqueous solutions ranging in pH from 2.2 to 8.2 in the absence of chemical or mechanical dissolution of the surface oxide. Friction is observed to vary with solution pH, and the specific manner in which interfacial friction depends on pH is influenced by the composition of the interface. The maximum friction force of the tungsten/silicon nitride system occurs at a pH of 4.7. The tungsten/alumina system has a maximum in the frictional force at a pH of 6.6. Frictional variations in these systems are related to pH-mediated changes in the electrostatic interaction between the probe tip and the sample. The pH dependence of the electrostatic interaction is determined by the relative isoelectric points of the contacting surfaces. These nanometer-scale measurements demonstrate a fundamental pathway by which variations...

Silicon nanoparticle synthesis by short-period thermal anneals at atmospheric pressure in argon

Silicon nanoparticles have been studied for a wide variety of applications including nanoelectronic, photovoltaic, and optoelectronic devices. In this work, silicon nanoparticles were synthesized by short-period annealing of silicon-on-insulator substrates to temperatures ranging between 600 and 900 °C in argon gas at atmospheric pressure. Two different top silicon layers were deposited by ion-beam sputtering onto oxidized substrates. The thinner 6 nm top layer samples were annealed to temperatures for 30 s periods while thicker 15 nm top layer samples were annealed for 60 s periods. For both sets of samples, nanoparticles were observed to form at all the anneal temperatures through imaging by AFM. One long-period UHV anneal study, with 30-min anneal times, observed nanoparticle formation at temperatures similar to the current work while another similar long-period UHV anneal reported nanoparticle formation only above well-defined formation temperatures that depended upon the starting top layer thickness. In the current work, the average nanoparticle radius was found to increase both with the final anneal temperature and anneal period. For the highest anneal temperatures of the 6 nm top layer samples, a changing surface topography indicated that the thinner Si source layer was becoming depleted and the nanoparticle formation process was nearing completion. No such changes were observed for the thicker 15 nm samples at the same temperatures.Silicon nanoparticles have been studied for a wide variety of applications including nanoelectronic, photovoltaic, and optoelectronic devices. In this work, silicon nanoparticles were synthesized by short-period annealing of silicon-on-insulator substrates to temperatures ranging between 600 and 900 °C in argon gas at atmospheric pressure. Two different top silicon layers were deposited by ion-beam sputtering onto oxidized substrates. The thinner 6 nm top layer samples were annealed to temperatures for 30 s periods while thicker 15 nm top layer samples were annealed for 60 s periods. For both sets of samples, nanoparticles were observed to form at all the anneal temperatures through imaging by AFM. One long-period UHV anneal study, with 30-min anneal times, observed nanoparticle formation at temperatures similar to the current work while another similar long-period UHV anneal reported nanoparticle formation only above well-defined formation temperatures that depended upon the starting top layer thickness....

Synthesis, characterization, and investigation of a conformationally immobile calix[6]arene as a negative electron beam resist

Calixarenes of a variety of molecular weights and with several different functional attachments have been studied as high resolution, high contrast negative electron beam resists. In this article, results are presented for a new type of calixarene molecule to be used as an electron beam resist. The molecule differs from previous calixarene resists through the use of bridging groups to limit its conformational mobility and by having only a partial functionalization of the available phenol units with allyl groups to enhance the resist sensitivity. Both the sensitivity and contrast of the calixarene were measured. The measured contrast was found to be 4, while the sensitivity was 3.6mC∕cm2 which is comparable to other fully functionalized calix[6]arene resists. A closer comparison of this calixarene with similar calixarenes indicates that the measured sensitivity is better than would be expected for this partially functionalized molecule and that full functionalization might not be necessary to obtain a sign...