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Undergraduate


I teach the following undergraduate classes:
MSE 446 : Semiconductor Processing
MSE 435 : Corrosion and Degradation of Materials

Graduate


I teach the following graduate classes:
MSE 503: Applied Surface Chemistry
MSE 502: Research Proposal Preparation
MSE 546 : Semiconductor Processing
MSE 535 : Corrosion and Degradation of Materials
Laboratories and Centers

Electrochemical Laboratory:

PAR 2273 Potentiostat-Galvanostat-Electrochemical Impedance Analyzer
PAR 273 Potentiostat
Gamry Potentiostat
Solartron Frequency Response Analyzer
Maxtek Electrochemical Quartz Crystal Microbalance
Special Tool for Conducting Electrochemical-Mechanical Planarization
(ECMP) Experiments

Surface and Colloid Chemical Laboratory

Coulter Delsa Electrophoretic Light Scattering Instrument
Coulter N4 Plus Submicron Particle Size Analyzer
Brookhaven-Paar Electrokinetic Analyzer
Malvern Zetasizer (shared equipment)

Other Facilities

Prosys Megasonic Cleaning Equipment in the clean room of Micro/Nano Fabrication laboratory
Cavitation Threshold (CT) cell to investigate interaction of megasonic waves with process fluids
Gaertner Ellipsometer
Horiba Optical monitor for simultaneous measurement of ammonium hydroxide and hydrgen peroxide concentration in solutions


RESEARCH AREAS:


I : Wet chemical processing in integrated circuit manufacturing Fabrication of current generation (45 nm) integrated circuits involves more than one hundred wet chemical processing steps such as etching, cleaning, rinsing and drying. Some of the key challenges in processing include selectivity in etching of different kinds of materials, cleaning of films to remove sub- 100 nm particles while maintaining a low degree of surface roughness , cleaning without damage to structures and prevention/mitigation of corrosion. Professor Raghavan’s group has been active in this area for over two decades and focuses on using fundamental principles of colloid, surface and electrochemistry to provide solutions to existing problems and develop new methods, which are environmentally benign.

Current projects:

1. HIGH-DOSE IMPLANT RESIST STRIPPING (HDIS): ALTERNATIVES TO ASH/STRIP METHOD

In a standard CMOS process flow, two source/drain implant steps are used. Removal of resists exposed to ions during these steps is currently carried out by an oxygen plasma ash method followed by a wet stripping process. This ash/strip method suffers from many drawbacks; it is a high energy process, causes silicon loss (by oxidation) and dopant loss and creates particulate contamination. For the removal of resists exposed to ions during certain sensitive shallow implant steps, replacement of ash/strip process by ‘all’ wet chemical methods has been of great interest to the integrated circuit manufacturers.
The principal objective of the research project is to develop a chemical system that is effective at disrupting the carbonized crust on deep UV resist layers exposed to high dose ions (≥1015 /cm2) at temperature and pH conditions that are safe to operate and to enhance the overall EHS climate of resist stripping processes. Specifically, formulations based on catalyzed hydrogen peroxide (CHP) reactions will be explored.

Sponsor: SRC/SEMATECH Research center for Environmentally Benign Semiconductor
Manufacturing., University of Arizona

Graduate Student: Mr. Rajkumar Govindarajan


2. IMPROVEMENT OF ESH IMPACT OF BACK END OF LINE (BEOL) CLEANING FORMULATIONS USING IONIC LIQUIDS TO REPLACE TRADITIONAL SOLVENTS

Back End of Line (BEOL) cleaning steps account for more than thirty percent of the total number of cleaning steps encountered in the fabrication of integrated circuits. Semi-aqueous fluoride (SAF) solutions containing between 20 to 40% of organic solvents currently remain as formulations of choice for BEOL cleaning. One of the issues with the use of SAF solutions is that they generate a waste stream that is complex and difficult to treat. Improvement of the overall ESH impact of BEOL cleaning can be achieved by simplifying the formulation using a chemical, which has multifunctional properties, i.e. serve as a low vapor pressure solvent as well as a conductive medium, work as a corrosion inhibitor for metal, provide residue etching features and miscible with water to allow easy rinsing after cleaning. In this context, room temperature ionic liquids (RTIL) offer an interesting and environmentally benign alternative to traditional solvents. This research project will systematically evaluate the feasibility of using RTIL for cleaning of residues created by vapor phase etching.


Sponsor: SRC/SEMATECH Research center for Environmentally Benign Semiconductor
Manufacturing., University of Arizona

Graduate Students : Ms. Nandini Venkataraman and Mr. Dinesh Thanu

3. LOWERING THE ESH IMPACT OF HIGH-K AND METAL GATE-STACK SURFACE PREPARATION PROCESSES [Co-PIs: NISHI (Stanford),VERMEIRE(ASU) , SHADMAN(UA)]


The objective of this project is to find new chemistries, rinse methodologies, and reliable in-situ as well as post cleaning performance testing techniques that would lead to elimination and/or reduction in usage of hazardous cleaning chemicals, reduction in usage of water, chemicals, and energy, and gain in performance of high-k metal gate stacks. The project will focus on two areas: (1) Development of non-fluoride based chemical formulations to etch high-k materials without inducing galvanic corrosion between metal gate and, (2) On-wafer sensors to monitor rinsing and drying processes in an effort to reduce DI water consumption required for removing contaminants.


Sponsor: SRC/SEMATECH Research center for Environmentally Benign Semiconductor
Manufacturing., University of Arizona

Graduate Student: Undecided

4. OPTIMIZATION OF DILUTE AMMONIA-PEROXIDE-MIXTURES (APM) FOR HIGH VOLUME MANUFACTURING THROUGH SURFACE CHEMICAL INVESTIGATIONS
Co-PI: Prof. J. Zhang, Department of Mining Engineering
Ammonium hydroxide-hydrogen peroxide mixtures have been the dominant chemical formulations used for the removal of particles from surfaces during integrated circuit manufacturing. As originally developed in the seventies, this formulation contained 1 part of ammonium hydroxide (28%), 1 part of hydrogen peroxide (30%), and 5 parts of water and was used at 80 deg. C. The formulation works by oxidizing silicon and dissolving the formed silicon dioxide to remove the adhered particles. The 1:1:5 formulation at 70 deg. C etches silicon at a rate of ~0.25 nm/min, which is unacceptable for current fabrication schemes. The progressive shrinking of feature size of structures in devices has demanded that oxide and silicon loss per cleaning step be reduced to less than 1 Å per cleaning step. Additionally, this formulation is expensive due to evaporation losses and high cost of hydrogen peroxide. Many integrated circuit companies have resorted to the use of diluted APM to overcome these issues. Dilution increases process time and makes on- line monitoring of the concentration of ammonia and peroxide a challenging task. Additionally, the dilution ratio is picked empirically with no clearly established fundamental interrelationship between this ratio and particle removal efficiency (PRE). The removal of particles from surfaces is dependent on the force of adhesion of particles to surfaces and the extent to which the surface is etched by the chemical formulation.

The objective of this proposal is to establish a scientific basis for deciding on the optimal dilution ratio based on the value of the force of adhesion of particles to surfaces at different dilution ratios. When used in conjunction with information on the precise concentration of alkali and peroxide in dilute APM solution, the force information will immensely help in high volume manufacturing of integrated circuits.

SPONSOR: Intel Corporation
Graduate Student: Mr. Shariq Siddiqui

II: Corrosion Processes:

EFFECT OF MICROSTRUCTURE AND ELECTROCHEMICAL CHARACTERISTICS OF COPPER ALLOYS ON THEIR ANTIMICROBIAL PROPERTIES

Co-PIs: Prof. David Poirier and Prof. Chris Rensing

Investigations focused on understanding the mechanisms underlying the inactivation of certain bacteria by copper and certain copper alloys have shown that several solution based factors such as copper ion (Cu+ as well as Cu2+) toxicity and reactive oxygen species influence killing rates. Additionally, there is evidence that the kill rate of certain bacterial colonies is different for copper and certain copper alloys and pure copper is more effective. However, the effect of microstructure and electrochemical characteristics of copper based materials have received almost no attention. It is the purpose of this proposal to conduct preliminary investigations to better understand the role of substrate characteristics on bacterial inactivation.

Sponsor: Copper Development Association

RECENTLY COMPLETED PROJECTS

1. Distribution of Acoustic Pressure on Wafer and its Impact on Megasonic Cleaning

Co-PIs: Prof. P. Deymier (UA) and Prof. P. Khuri-Yakub (Stanford)
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Sponsor: Intel Corporation Graduate Students: Ms. Sangita Kumari and Ms. Janet Glenn 2. Electrochemical-Mechanical Planarization (ECMP)of Tantalum Barrier Layers
Sponsor: SRC-Sematech Center for Environmentally Benign Semiconductor Manufacturing,

University of Arizona
Graduate Students: Mr. Ashok Muthukumaran and Mr. Rajkumar Govindarajan

Selected Publications

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M. Keswani, S. Raghavan, P. Deymier, and S. Verhaverbeke, Megasonic cleaning of wafers in electrolyte solutions: Possible role of electro-acoustic and cavitation effects, Microelectronic Engineering, Vol 86, 132–139 (2009).

A. Muthukumaran, N. Venkataraman, S. Tamilmani and S. Raghavan, Anodic dissolution of copper in dilute hydroxylamine solutions: application to electrochemical mechanical planarisation of copper, Corrosion Engineering, Science and Technology Vol 44 (2) , pp.101-107 (2009).

A. Muthukumaran, N. Venkataraman and S. Raghavan, Evaluation of Sulfonic Acid based Solutions for Electrochemical Mechanical Removal of Tantalum, J. Electrochemical Society, Vol. 155 (3) , H184-187 (2008).

S. Balasubramanian and S. Raghavan, Wet Etching of Heat Treated Atomic Layer Chemical Vapor Deposited Zirconium Oxide in HF Based Solutions, Japanese Journal of Applied Physics, Vol. 47 (6), pp. 4502-4504 (2008).

S. Raghavan, M. Keswani and R. Jia, Particulate Science and Technology in the Engineering of Slurries for Chemical Mechanical Planarization, KONA Powder and Particle Journal, No.26 , pp. 94-105 (2008).

K. Valenzuela, S. Raghavan, P. A. Deymier. and J. Hoying, Formation of Copper Nanowires by Electroless Deposition Using Microtubules as Templates, Journal of Nanoscience and Nanotechnology, Vol. 8, Number 7, pp. 3416-3421 (2008).


EMPLOYMENT OF RECENT GRADUATES: Dr. M. Keswani (INTEL)
Mr. J. Diaz (University of Panama)
Dr. A. Muthukumaran (INTEL)
Dr. V. Lowalekar (INTEL)
Dr. V. Pandit (NOVELLUS)
Dr. S. Kondoju (MICRON)
Mr. H. Shende (MICRON)