Oxalic Acid Based Chemical Systems for Electrochemical Mechanical Planarization of Copper

Persistent Link:
http://hdl.handle.net/10150/193886
Title:
Oxalic Acid Based Chemical Systems for Electrochemical Mechanical Planarization of Copper
Author:
Lowalekar, Viral Pradeep
Issue Date:
2006
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:
In an ECMP process, a wafer is anodically baised during polishing. The electrical potential is the driving force to oxidize copper metal to ions. Copper ions then react with chemistry in the electrolyte to go in solution or form a passivation layer on the surface. The passivation layer is removed by a very low downforce (0.5-1 psi), causing copper to electrochemically dissolve in solution. Passive film formation during copper ECMP is key to the success of this process, since passivation reduces dissolution in the recessed areas, while elevations on the copper surface in direct contact with the ECMP pad are electrochemically planarized. If no passive film forms, then copper removal will be conformal from the elevated and recessed areas, and planarity will be lost. Chemical formulations for the electrochemical mechanical planarization (ECMP) of copper must contain constituents that are stable at anodic potentials. A key component of the formulation is a corrosion inhibitor, which is required to protect low lying areas while higher areas are selectively removed. Organic compounds, which adsorb on copper at low overpotentials and form a film by oxidation at higher overpotentials, may be particularly useful for ECMP. The main goal of the research reported in this dissertation is to understand and develop oxalic acid-based chemical systems suitable for ECMP of copper through electrochemical and surface investigations. Special attention was paid to the development of an inhibitor, which can function under applied potential conditions. Physical methods such as profilometry and four point probe were used to obtain copper removal rates. An organic compound, thiosalicylic acid (TSA), was identified and tested as a potential corrosion inhibitor for copper. TSA offers better protection than the conventionally used benzotriazole (BTA) by oxidizing at high anodic potentials to form a passive film on the copper surface. The passive film formed on the copper surface by addition of TSA was characterized by X-ray photoelectron spectroscopy. The oxidation potential of TSA was characterized using cyclic voltammetry. The passivation and repassivation kinetics was investigated in detail and a passivation mechanism of copper in oxalic acid in the presence of TSA is proposed. Copper removal experiments were performed on a specially designed electrochemical abrasion cell (EC-AC) in both the presence and absence of inhibitors. The effect of anodic potentials on the dissolution of copper was studied to identify suitable conditions for the electro-chemical mechanical planarization process.
Type:
text; Electronic Dissertation
Keywords:
Planarization; Copper; CMP; ECMP
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.titleOxalic Acid Based Chemical Systems for Electrochemical Mechanical Planarization of Copperen_US
dc.creatorLowalekar, Viral Pradeepen_US
dc.contributor.authorLowalekar, Viral Pradeepen_US
dc.date.issued2006en_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.abstractIn an ECMP process, a wafer is anodically baised during polishing. The electrical potential is the driving force to oxidize copper metal to ions. Copper ions then react with chemistry in the electrolyte to go in solution or form a passivation layer on the surface. The passivation layer is removed by a very low downforce (0.5-1 psi), causing copper to electrochemically dissolve in solution. Passive film formation during copper ECMP is key to the success of this process, since passivation reduces dissolution in the recessed areas, while elevations on the copper surface in direct contact with the ECMP pad are electrochemically planarized. If no passive film forms, then copper removal will be conformal from the elevated and recessed areas, and planarity will be lost. Chemical formulations for the electrochemical mechanical planarization (ECMP) of copper must contain constituents that are stable at anodic potentials. A key component of the formulation is a corrosion inhibitor, which is required to protect low lying areas while higher areas are selectively removed. Organic compounds, which adsorb on copper at low overpotentials and form a film by oxidation at higher overpotentials, may be particularly useful for ECMP. The main goal of the research reported in this dissertation is to understand and develop oxalic acid-based chemical systems suitable for ECMP of copper through electrochemical and surface investigations. Special attention was paid to the development of an inhibitor, which can function under applied potential conditions. Physical methods such as profilometry and four point probe were used to obtain copper removal rates. An organic compound, thiosalicylic acid (TSA), was identified and tested as a potential corrosion inhibitor for copper. TSA offers better protection than the conventionally used benzotriazole (BTA) by oxidizing at high anodic potentials to form a passive film on the copper surface. The passive film formed on the copper surface by addition of TSA was characterized by X-ray photoelectron spectroscopy. The oxidation potential of TSA was characterized using cyclic voltammetry. The passivation and repassivation kinetics was investigated in detail and a passivation mechanism of copper in oxalic acid in the presence of TSA is proposed. Copper removal experiments were performed on a specially designed electrochemical abrasion cell (EC-AC) in both the presence and absence of inhibitors. The effect of anodic potentials on the dissolution of copper was studied to identify suitable conditions for the electro-chemical mechanical planarization process.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectPlanarizationen_US
dc.subjectCopperen_US
dc.subjectCMPen_US
dc.subjectECMPen_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.committeememberDavenport, Williamen_US
dc.contributor.committeememberPoirier, Daviden_US
dc.identifier.proquest1778en_US
dc.identifier.oclc659747540en_US
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