Chemical Systems for Electrochemical Mechanical Planarization of Copper and Tantalum Films

Persistent Link:
http://hdl.handle.net/10150/194160
Title:
Chemical Systems for Electrochemical Mechanical Planarization of Copper and Tantalum Films
Author:
Muthukumaran, Ashok Kumar
Issue Date:
2008
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Electro-Chemical Mechanical Planarization (ECMP) is a new and highly promising technology just reaching industrial application; investigation of chemistries, consumables, and tool/control approaches are needed to overcome technological limitations. Development of chemical formulations for ECMP presents several challenges. Unlike conventional CMP, formulations for ECMP may not need an oxidant. Organic additives, especially inhibitors used to control planarity (i.e. to protect recessed regions), need to be stable under applied anodic potential. To have a high current efficiency, the applied current should not induce decomposition of the formulations. In addition, to enable clearing of the copper film, the interactions between multiple exposed materials (barrier material as well as copper) must be considered. Development of a full sequence ECMP process would require the removal of the barrier layer as well. Chemical systems that exhibit a 1:1 selectivity between the barrier layer and copper would be ideal for the barrier removal step of ECMP. The main goal of this research is to investigate the chemistries suitable for ECMP of copper and tantalum films. Copper was electroplated onto the gold electrode of quartz crystals, and its dissolution/passivation behavior in hydroxylamine solutions was studied at different applied potential values. The dissolution rate of copper is pH dependent and exhibits a maximum in the vicinity of pH 6. Copper dissolution increases with respect to overpotential (η) and dissolution rates as high as 6000 Å/min have been obtained at overpotential of 750mV. While both benzotriazole (BTA) and salicylhydroxamic acid (SHA) serve as good inhibitors at lower overpotentials, their effectiveness decreases at higher overpotentials. A fundamental study was undertaken to evaluate the usefulness of a sulfonic acid based chemical system for the removal of tantalum under ECMP conditions. Tantalum as well as copper samples were polished at low pressures (~0.5 psi) under galvanostatic conditions in dihydroxy benzene sulfonic acid (DBSA) solutions maintained at different pH values. At a current density of 0.5 mA/cm² and a pH of 10, tantalum removal rate of 200 Å/min with a 1:1 selectivity to copper was obtained in 0.3M DBSA solutions containing 1.2M H₂O₂. The presence of a small amount (~ 0.1%) of colloidal silica particles was required to obtain good removal rates. A comparison of DBSA and methane sulfonic acid (MSA) based chemical system was studied for the removal of tantalum. The performance of DBSA is better than that of MSA. Additionally, DBSA solution has been used for tantalum nitride removal under ECMP conditions. However, DBSA is not as effective for tantalum nitride as it is for tantalum. Polishing of the patterned test structure in optimized solution containing 0.01M BTA results in complete removal of barrier layer and surface planarity is achieved.
Type:
text; Electronic Dissertation
Keywords:
Electrochemical Mechanical Planarization (ECMP); Copper; Tantalum
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Materials Science & Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Raghavan, Srini
Committee Chair:
Raghavan, Srini

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleChemical Systems for Electrochemical Mechanical Planarization of Copper and Tantalum Filmsen_US
dc.creatorMuthukumaran, Ashok Kumaren_US
dc.contributor.authorMuthukumaran, Ashok Kumaren_US
dc.date.issued2008en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractElectro-Chemical Mechanical Planarization (ECMP) is a new and highly promising technology just reaching industrial application; investigation of chemistries, consumables, and tool/control approaches are needed to overcome technological limitations. Development of chemical formulations for ECMP presents several challenges. Unlike conventional CMP, formulations for ECMP may not need an oxidant. Organic additives, especially inhibitors used to control planarity (i.e. to protect recessed regions), need to be stable under applied anodic potential. To have a high current efficiency, the applied current should not induce decomposition of the formulations. In addition, to enable clearing of the copper film, the interactions between multiple exposed materials (barrier material as well as copper) must be considered. Development of a full sequence ECMP process would require the removal of the barrier layer as well. Chemical systems that exhibit a 1:1 selectivity between the barrier layer and copper would be ideal for the barrier removal step of ECMP. The main goal of this research is to investigate the chemistries suitable for ECMP of copper and tantalum films. Copper was electroplated onto the gold electrode of quartz crystals, and its dissolution/passivation behavior in hydroxylamine solutions was studied at different applied potential values. The dissolution rate of copper is pH dependent and exhibits a maximum in the vicinity of pH 6. Copper dissolution increases with respect to overpotential (η) and dissolution rates as high as 6000 Å/min have been obtained at overpotential of 750mV. While both benzotriazole (BTA) and salicylhydroxamic acid (SHA) serve as good inhibitors at lower overpotentials, their effectiveness decreases at higher overpotentials. A fundamental study was undertaken to evaluate the usefulness of a sulfonic acid based chemical system for the removal of tantalum under ECMP conditions. Tantalum as well as copper samples were polished at low pressures (~0.5 psi) under galvanostatic conditions in dihydroxy benzene sulfonic acid (DBSA) solutions maintained at different pH values. At a current density of 0.5 mA/cm² and a pH of 10, tantalum removal rate of 200 Å/min with a 1:1 selectivity to copper was obtained in 0.3M DBSA solutions containing 1.2M H₂O₂. The presence of a small amount (~ 0.1%) of colloidal silica particles was required to obtain good removal rates. A comparison of DBSA and methane sulfonic acid (MSA) based chemical system was studied for the removal of tantalum. The performance of DBSA is better than that of MSA. Additionally, DBSA solution has been used for tantalum nitride removal under ECMP conditions. However, DBSA is not as effective for tantalum nitride as it is for tantalum. Polishing of the patterned test structure in optimized solution containing 0.01M BTA results in complete removal of barrier layer and surface planarity is achieved.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectElectrochemical Mechanical Planarization (ECMP)en_US
dc.subjectCopperen_US
dc.subjectTantalumen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineMaterials Science & Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorRaghavan, Srinien_US
dc.contributor.chairRaghavan, Srinien_US
dc.contributor.committeememberLucas, Pierreen_US
dc.contributor.committeememberParks, Harold G.en_US
dc.identifier.proquest2554en_US
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