Chris Rogers | Tufts University (original) (raw)
Chris got all three of his degrees at Stanford Univ., where he worked with John Eaton on his thesis looking at particle motion in a boundary layer flow. From Stanford, he went to Tufts as a faculty member, where he has been for the last million years, with a few exceptions. His first sabbatical was spent at Harvard and a local kindergarten looking at methods of teaching engineering. He spent half a year in New Zealand on a Fulbright Scholarship looking at 3D reconstruction of flame fronts to estimate heat fluxes. In 2002-3 he was at Princeton as the Kenan Professor of Distinguished Teaching where he played with underwater robots, wind tunnels, and LEGO bricks. In 2006-7, he spent the year at ETH in Zurich playing with very very small robots and measuring the lift force on a fruit fly. He received the 2003 NSF Director’s Distinguished Teaching Scholar Award for excellence in both teaching and research. Chris is involved in several different research areas: particle-laden flows (a continuation of his thesis), telerobotics and controls, slurry flows in chemical-mechanical planarization, the engineering of musical instruments, measuring flame shapes of couch fires, measuring fruit-fly locomotion, and in elementary school engineering education. His work has been funded by numerous government organizations and corporations, including the NSF, NASA, Intel, Boeing, Cabot, Steinway, Selmer, National Instruments, Raytheon, Fulbright, and the LEGO Corporation. His work in particle-laden flows led to the opportunity to fly aboard the NASA 0g experimental aircraft. He has flown over 700 parabolas without getting sick.
Chris also has a strong commitment to teaching, and at Tufts has started a number of new directions, including learning robotics with LEGO bricks and learning manufacturing by building musical instruments. He was awarded the Carnegie Professor of the Year in Massachusetts in 1998 and is currently the director of the Center for Engineering Education Outreach (www.ceeo.tufts.edu). His teaching work extends to the elementary school, where he talks with over 1000 teachers around the world every year on ways of bringing engineering into the younger grades. He has worked with LEGO to develop ROBOLAB, a robotic approach to learning science and math. ROBOLAB has already gone into over 50,000 schools worldwide and has been translated into 15 languages. He has been invited to speak on engineering education in Singapore, Hong Kong, Australia, New Zealand, Denmark, Sweden, Norway, Luxembourg, Switzerland, the UK, and in the US. He works in various classrooms once a week, although he has been banned from recess for making too much noise.
Most importantly, he has three kids - all brilliant - who are responsible for most of his research interests and efforts.
Supervisors: John Eaton
Phone: 617 627 2882
Address: 200 College Ave
Medford, MA
02155
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Papers by Chris Rogers
33rd Aerospace Sciences Meeting and Exhibit, 1995
34th Aerospace Sciences Meeting and Exhibit, 1996
In this paper a method of quantifying fluid mixing using the fluorescence intensity of fluorophor... more In this paper a method of quantifying fluid mixing using the fluorescence intensity of fluorophors in aqueous solution is presented. The general technique involves ratioing optically separable fluorescence from two fluorescent dyes. The resulting ratio normalizes for laser intensity distribution and any laser reflections. By properly selecting the fluorescent dyes, fluorescence ratios can be used to either measure the concentration of a passive scalar or temperature fields. In this study, fluorescence ratios were used to quantify the hydronium ion concentration of mixing fluids in a two dimensional plane. This was accomplished by temporally and spatially synchronizing two CCD cameras to simultaneously image laser induced fluorescence. Single and multi-dye systems were examined for their accuracy in predicting mixing and of the dye systems examined, a fluorescein rhodamine B solution proved to be the most accurate. Using this dye system, the fluorescence ratios were found to vary under 1 standard deviation for a 2.5 fold change in laser power. A standard error of under 6% of the mean fluorescence ratio was typical. This system was demonstrated by measuring the mixing in an axis-symmetric turbulent jet with an Reynolds number of 9,000. Finally, this technique was shown to be capable of measuring temperature fields.
Experiments in Fluids, 1998
In this paper, a new method of measuring scalar behavior in bulk aqueous fluid flows is presented... more In this paper, a new method of measuring scalar behavior in bulk aqueous fluid flows is presented. Using a simple ratiometric scheme, laser induced fluorescence from organic dyes can be normalized so that direct measurements of a scalar in the flow are possible. The technique dual emission laser induced fluorescence (DELIF) relies on normalizing the fluorescence emission intensity of one dye with the fluorescence emission intensity of a second dye. Since each dye fluoresces at a different wavelength, one can optically separate the emission of each dye. This paper contains an overview of the basic ratiometric technique for pH and temperature measurements as well as the spectral properties of nine water soluble dyes. It also covers the three most significant sources of error in DELIF applications. To demonstrate the technique, steady state turbulent jet mixing and temperature fields in a thermal plume were quantified. The accuracy was camera limited at under 3% of the fluorescence ratio which corresponds to 0.1 pH units or 1.8°C.
MRS Proceedings, 2003
This paper presents temperature and friction force data at the pad-slurry-wafer interface during ... more This paper presents temperature and friction force data at the pad-slurry-wafer interface during real time CMP polishing with in situ pad conditioning. Experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer down force control. Dual emission laser induced fluorescence (DELIF) techniques are used to optically measure the temperature directly beneath the wafer during polishing using a two camera imaging system. An infrared camera and a thermocouple are alternately used to measure bow wave temperatures. Optically transparent BK-7 glass wafers with either concave (wafer edges sloping toward the pad) or convex (wafer edges sloping away from the pad) curvature were used. When concave wafers are polished, the bow wave temperatures are 3°C to 5°C higher than the corresponding value for convex wafers. Similarly, slurry temperatures under the concave wafers are 5°C to 6°C higher than the value for convex wafers (±0.5°C). The friction forc...
MRS Proceedings, 1996
Chemical‐Mechanical Polishing (CMP) is one of the fastest growing market segments in the semicond... more Chemical‐Mechanical Polishing (CMP) is one of the fastest growing market segments in the semiconductor equipment industry. One of the critical consumable in CMP is a specialized solution, or slurry, which contains both free abrasives and chemicals acting together to planarize a wafer. These chemically active slurries account for approximately one fifth of the total cost of polishing a wafer. Because of the cost and potential toxicity, there are both financial and environmental pressures to reduce the amount of slurry consumed during the CMP process. To accomplish this in a systematic manner we have developed a technique for quantifying slurry flow patterns during CMP which involves using fluorescent dyes to measure slurry mixing, temperature gradients and slurry aging during the polishing. An aqueous fluorescent solution with matching viscosity is used to model the slurry, a glass window models the wafer and a commercially available polisher provides the polishing pad/table rotating...
MRS Proceedings, 2007
ABSTRACTIt is becoming increasingly clear that understanding the small scale polishing mechanisms... more ABSTRACTIt is becoming increasingly clear that understanding the small scale polishing mechanisms operating during CMP requires knowledge of the nature of the pad-wafer contact. Dual Emission Laser Induced Fluorescence (DELIF) can be used to study the fluid layer profile between the polishing pad and the wafer during CMP. Interactions between the polishing pad surface and the wafer can then be deduced from the fluid layer profile. Previous investigations of pad-wafer interactions using DELIF include in-situ measurements of average fluid layer thickness and asperity layer compressibility, surface roughness measurements and polishing pad rebound into etched wells. In this paper, DELIF is used to determine pad-wafer contact, the point at the fluid film thickness goes to zero. We present a technique and some preliminary data for instantaneous measurement of in-situ pad-wafer contact using DELIF. The imaging area is 1.30×1.74 mm with a resolution of 2.5 μm/pixel. At this magnification, s...
MRS Proceedings, 2004
Duel Emission Laser Induced Fluorescence (DELIF) and friction measurements are taken in-situ duri... more Duel Emission Laser Induced Fluorescence (DELIF) and friction measurements are taken in-situ during CMP to observe slurry flow beneath a model of an integrated circuit (IC) wafer. Friction measurements average around 7.5 lb and multiple frequencies are observed. Slurry film thicknesses on the order of a 10±3μm were observed during CMP of a flat wafer. The film thickness seems uncorrelated to friction measurements except when the pad and wafer rotation speeds are significantly slowed. DELIF has also accurately measured a 9μm etched step, with noise in the image equal to ±3 μm.
World Tribology Congress III, Volume 2, 2005
Modifications to the Dual Emission Laser Induced Fluorescence (DELIF) procedure used to collect i... more Modifications to the Dual Emission Laser Induced Fluorescence (DELIF) procedure used to collect images of the slurry layer between the polishing pad and wafer during Chemical Mechanical Planarization (CMP) have provided a means to attain instantaneous, high spatial resolution images of slurry film thickness. Presented here is a technique to determine the calibration factor that correlates image intensity to slurry film thickness. This presentation will discuss how to determine slurry layer shape near wafer features, pad roughness, and pad compressibility.
Tribology Letters, 2008
To test the accuracy of optically measuring contact, we examined the height distribution histogra... more To test the accuracy of optically measuring contact, we examined the height distribution histogram of a simulated rough surface contacting a smooth surface. We qualified the technique sensitivity as a function of the inverse signal-to-noise ratio having values ranging from 0 to 0.3. An explanation of how the analysis technique can be applied to Dual Emission Laser-Induced Fluorescence (DELIF) measurements is provided.
Journal of Science Education and Technology, 2011
We report results and impressions from a three-day inquiry-based workshop for K-8 teachers, aimed... more We report results and impressions from a three-day inquiry-based workshop for K-8 teachers, aimed at improving their understanding of energy from a science and engineering perspective. Results suggest that the teachers made significant gains in understanding and appreciation of important energy concepts, but their comprehension of some key ideas remained incomplete. The dissipation of energy into thermal energy of the environment proved to be a particularly difficult idea, and one that represents a serious obstacle to understanding the principle of the conservation of energy.
Journal of Engineering Education, 1997
Combining LEGO® Dacta building blocks with LabVIEW TM software produced a highly successful, low-... more Combining LEGO® Dacta building blocks with LabVIEW TM software produced a highly successful, low-cost (less than $500 per station excluding computer) alternative method of teaching engineering through hands-on experimentation. Dubbed LEGO® Data Acquisition and Prototyping System (or LDAPS), this combination of tools provides a highly capable workbench for students, yet brings a new level of creativity and fun into teaching engineering at the college level. In this paper we present the methodology and describe one class where it is currently in use. Student, faculty, and staff response to the class was very positive, partly due to the popularity of hands-on engineering and partly because LEGO® blocks allow the students to exercise their creativity and innovation. The strength in the LDAPS methodology lies in the power of the LEGO® bricks and the LabVIEW TM software. LEGO® motors, sensors, and bricks are almost infinitely configurable, making each experiment unique. LabVIEW TM is a powerful, visual programming language in which students can perform advanced signal processing with relatively few programming skills. We are currently extending this methodology to teach engineering to liberal arts majors as well as precollege students.
Journal of The Electrochemical Society, 2000
In order to better understand the role of the uid behavior in CMP, we measured slurry transport b... more In order to better understand the role of the uid behavior in CMP, we measured slurry transport beneath a glass wafer. We quanti ed the slurry transport using Residence Time Distribution techniques and two measures of slurry transport e ciency de ned as the percentage of new slurry beneath a wafer. Slurry transport e ciency depended on platen speed, ow rate, and the conditioning method. We found that the average uid residence times under the wafer decreased roughly linearly with platen speed. A threefold increase in platen speed decreased slurry mean residence times by three and a half times. Changing the ow rate from 20 cc min to 50 cc min decreased the slurry mean residences by 80. In situ conditioning generally increased the slurry mean residence times and the amount of slurry mixing. In situ conditioning also decreased gradients in the slurry composition across the wafer. Pad topography had a large e ect on the slurry gradients that developed across the wafer. Finally, w e found that the slurry mixing history can be accurately modeled using a simple continuous function.
Journal of The Electrochemical Society, 2005
In situ fluid film pressure and interfacial friction measurements during chemical mechanical plan... more In situ fluid film pressure and interfacial friction measurements during chemical mechanical planarization ͑CMP͒ are reported over a range of applied loads ͑27.6-41.4 kPA or 4-6 psi͒ and relative pad/wafer velocities ͑0.35-0.58 m/s͒. The slurry film pressure beneath contoured test wafers was measured using a novel experimental setup that enables dynamic data collection. The friction data have a repeatability of ϳ10%. The uncertainty of the pressure measurements and the computed down forces were ±2.1 kPa͑±0.3 psi͒ and 20%, respectively. The data indicate that wafer shape, specifically global curvature, is a significant factor in determining the lubrication regime during CMP. Full hydrodynamic lubrication, in which the slurry fluid film supports the entire applied load, was not realized for either concave ͑center high͒ or convex ͑center low͒ wafers. The data for concave wafers show that −6% to 37% of the applied load is supported by the slurry film, where the negative sign indicates suction conditions that were obtained at the lowest applied load condition. CMP of convex wafers is found to operate closer to full hydrodynamic lubrication, with the fluid layer supporting 36% to 64% of the applied downforce. In all cases, the measured friction coefficient decreased as the support of the fluid layer increased ͑higher positive pressures͒. CMP of concave wafers is more sensitive to changes in applied downforce, while the convex wafer type was most affected by changes in the wafer/pad rotation speed, which in turn determines effective slurry film velocity beneath the wafer. Overall, the CMP conditions seen in these scaled experiments operate primarily in the partial lubrication regime shifting closer to hydrodynamic lubrication for convex wafers at the high load, high speed conditions.
Journal of The Electrochemical Society, 2009
The objective of this work is to obtain in situ slurry fluid flow data during the chemical mechan... more The objective of this work is to obtain in situ slurry fluid flow data during the chemical mechanical planarization ͑CMP͒ process. Slurry flow affects the material removal processes, the creation of defects, and consumable use during CMP, and therefore impacts the cost and quality of polishing. Wafer-scale flow visualization using seeded slurry was accomplished for a variable applied load ͑0.3-2.5 psi downforce͒, wafer rotation speed ͑0 and 33 rpm͒, slurry injection locations, and various pad types ͑flat, XY grooved, and AC grooved͒. In situ pad conditioning was employed in all experiments. The data indicated complex slurry flow fields on the pad surface in the wafer vicinity, which are influenced by slurry injection point, pad grooving, downforce, and wafer/conditioner rotation. Injection location and pad type were shown to have the strongest impact on the variation in the fluid flow fields obtained.
Journal of The Electrochemical Society, 2004
Chemical mechanical planarization ͑CMP͒ is a process widely used for the manufacture of silicon i... more Chemical mechanical planarization ͑CMP͒ is a process widely used for the manufacture of silicon integrated circuits. In this work, we measured the thickness of the slurry film between the wafer and the pad during polish while simultaneously measuring the frictional drag. All experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer downforce control. Dual emission laser-induced fluorescence techniques optically measured the slurry film thickness through a dual-camera imaging system. The resulting data are discussed for wafers polished with a 3.1 wt % abrasive concentration slurry solution on Freudenberg's FX-9 polishing pads. It was found that the degree of surface curvature of the wafer substrate significantly influences the slurry film thickness and wafer drag, and therefore, the polish. The convex wafer shows the expected behavior of increased downforce reduces the slurry film thickness and increases the coefficient of friction. Further, as the pad speeds up, the slurry thickness increases and the friction decreases. The concave wafer shows no change in slurry film thickness and a decrease in the frictional coefficient with increasing downforce. Both the film thickness and frictional coefficient appear to decrease slightly with increasing pad speed. This difference between the two wafer shapes reflects the different fluid mechanics in each case.
Journal of The Electrochemical Society, 2009
Achieving device-and wafer-scale planarity in integrated circuit manufacturing is increasingly ch... more Achieving device-and wafer-scale planarity in integrated circuit manufacturing is increasingly challenging as device sizes are reduced to 35 nm and smaller, and wafer sizes are increased from 300 to 450 mm. Hence a better understanding of chemical mechanical planarization ͑CMP͒ processes is needed. We report the synchronous, in situ measurement of wafer forces ͓coefficient of friction ͑CoF͔͒ and wafer orientation during CMP polishing of BK7 glass wafers and the ex situ measurement of material removal rate ͑MRR͒ over a wide range of applied vertical loads and relative rotational velocities. MRR appears to be Prestonian and was significantly reduced by moving the slurry injection location to the outer edge of the wafer track leading to slurry starvation. Both positive and negative wafer pitch angles were measured, indicating that apparently contradictory modeling reports in the literature may not be in conflict. A phenomenological linkage between wafer orientation and frictional behavior was observed with positive pitch angles ͑from +0.2 to +0.4°͒ corresponding to smooth polishing and nose-down angles ͑from −0.2 to +0.2°͒ corresponding to stick-slip. Spectral signal analysis shows that the variation of CoF is due to platen rotation effects, while wafer orientation variation is affected by both platen and wafer rotations.
Experiments in Fluids, 2011
Dual emission laser induced fluorescence (DELIF) is a technique for measuring the instantaneous t... more Dual emission laser induced fluorescence (DELIF) is a technique for measuring the instantaneous thin fluid film thickness in dynamic systems. Two fluorophores within the system produce laser induced emissions that are filtered and captured by two cameras. The ratio of the images from these cameras is used to cancel the effect of the laser beam profile on the image intensity. The resultant intensity ratio can be calibrated to a fluid film thickness. The utilization of a 2-dye system when applied to Chemical Mechanical Polishing (CMP) is complicated by the fluorescence of the polymeric polishing pad and the light scattering particles in the polishing slurry. We have developed a model of DELIF for CMP with 1-dye employing the polishing pad as the second fluorophore. While scattering particles in the slurry decrease the overall intensity of the individual images, the contrast in the image ratio increases. Using the 1-dye DELIF system to measure thin slurry films, our model results indicate that a cubic calibration may be needed. However, experimental results suggest a linear calibration is achieved for slurry films between 0 and 133 lm thick with scattering coefficients as high as 8.66 mm-1 at a wavelength equal to 410 nm.
Electrochemical and Solid-State Letters, 2005
Recent experimental advances using Dual Emission Laser Induced Fluorescence (DELIF) and image pro... more Recent experimental advances using Dual Emission Laser Induced Fluorescence (DELIF) and image processing have provided high spatial and temporal resolution maps of the slurry layer during Chemical Mechanical Polishing (CMP). Intensity differences in the images correspond to fluid layer thickness variations as the slurry passes between different pad and wafer topographies. Asperities expand under 14µm deep wells and are compressed beyond the trailing edge of the well. Air pockets travel from the leading to the trailing edge of the wafer through 27µm deep wells. The pads tested were Freudenberg FX9, Rodel IC1000, and experimental pads from Cabot Microelectronics.
Electrochemical and Solid-State Letters, 2010
As semiconductor device sizes continue to shrink and economic realities drive ever increasing yie... more As semiconductor device sizes continue to shrink and economic realities drive ever increasing yield targets, achieving wafer scale planarity through the application of chemical mechanical planarization ͑CMP͒ has become increasingly challenging. The dynamics of the wafer-pad interface is critical to maintaining this uniformity. Utilizing measured friction coefficients ͑0.3-0.6͒, we report on the transitions from a smooth planarization regime to a stick-slip regime and vice versa over a set of two applied vertical loads and three relative velocities during the CMP process. Finally, we note a correlation between time spent in a stick-slip regime and platen velocity.
Micromachined structures with diameters ranging from 50-100 µm have been applied to the measureme... more Micromachined structures with diameters ranging from 50-100 µm have been applied to the measurement of the microscale shearing forces present at the wafer-pad interface during chemical mechanical polishing (CMP). The structures are 80 µm high poly-dimethyl-siloxane posts with bending stiffnesses ranging from 1.6 to 14 µN/µm. The structures were polished using a stiff, ungrooved pad and 3 wt% fumed silica slurry at relative velocities of approximately 0.5 m/s and downforces of approximately 1 psi. ...
33rd Aerospace Sciences Meeting and Exhibit, 1995
34th Aerospace Sciences Meeting and Exhibit, 1996
In this paper a method of quantifying fluid mixing using the fluorescence intensity of fluorophor... more In this paper a method of quantifying fluid mixing using the fluorescence intensity of fluorophors in aqueous solution is presented. The general technique involves ratioing optically separable fluorescence from two fluorescent dyes. The resulting ratio normalizes for laser intensity distribution and any laser reflections. By properly selecting the fluorescent dyes, fluorescence ratios can be used to either measure the concentration of a passive scalar or temperature fields. In this study, fluorescence ratios were used to quantify the hydronium ion concentration of mixing fluids in a two dimensional plane. This was accomplished by temporally and spatially synchronizing two CCD cameras to simultaneously image laser induced fluorescence. Single and multi-dye systems were examined for their accuracy in predicting mixing and of the dye systems examined, a fluorescein rhodamine B solution proved to be the most accurate. Using this dye system, the fluorescence ratios were found to vary under 1 standard deviation for a 2.5 fold change in laser power. A standard error of under 6% of the mean fluorescence ratio was typical. This system was demonstrated by measuring the mixing in an axis-symmetric turbulent jet with an Reynolds number of 9,000. Finally, this technique was shown to be capable of measuring temperature fields.
Experiments in Fluids, 1998
In this paper, a new method of measuring scalar behavior in bulk aqueous fluid flows is presented... more In this paper, a new method of measuring scalar behavior in bulk aqueous fluid flows is presented. Using a simple ratiometric scheme, laser induced fluorescence from organic dyes can be normalized so that direct measurements of a scalar in the flow are possible. The technique dual emission laser induced fluorescence (DELIF) relies on normalizing the fluorescence emission intensity of one dye with the fluorescence emission intensity of a second dye. Since each dye fluoresces at a different wavelength, one can optically separate the emission of each dye. This paper contains an overview of the basic ratiometric technique for pH and temperature measurements as well as the spectral properties of nine water soluble dyes. It also covers the three most significant sources of error in DELIF applications. To demonstrate the technique, steady state turbulent jet mixing and temperature fields in a thermal plume were quantified. The accuracy was camera limited at under 3% of the fluorescence ratio which corresponds to 0.1 pH units or 1.8°C.
MRS Proceedings, 2003
This paper presents temperature and friction force data at the pad-slurry-wafer interface during ... more This paper presents temperature and friction force data at the pad-slurry-wafer interface during real time CMP polishing with in situ pad conditioning. Experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer down force control. Dual emission laser induced fluorescence (DELIF) techniques are used to optically measure the temperature directly beneath the wafer during polishing using a two camera imaging system. An infrared camera and a thermocouple are alternately used to measure bow wave temperatures. Optically transparent BK-7 glass wafers with either concave (wafer edges sloping toward the pad) or convex (wafer edges sloping away from the pad) curvature were used. When concave wafers are polished, the bow wave temperatures are 3°C to 5°C higher than the corresponding value for convex wafers. Similarly, slurry temperatures under the concave wafers are 5°C to 6°C higher than the value for convex wafers (±0.5°C). The friction forc...
MRS Proceedings, 1996
Chemical‐Mechanical Polishing (CMP) is one of the fastest growing market segments in the semicond... more Chemical‐Mechanical Polishing (CMP) is one of the fastest growing market segments in the semiconductor equipment industry. One of the critical consumable in CMP is a specialized solution, or slurry, which contains both free abrasives and chemicals acting together to planarize a wafer. These chemically active slurries account for approximately one fifth of the total cost of polishing a wafer. Because of the cost and potential toxicity, there are both financial and environmental pressures to reduce the amount of slurry consumed during the CMP process. To accomplish this in a systematic manner we have developed a technique for quantifying slurry flow patterns during CMP which involves using fluorescent dyes to measure slurry mixing, temperature gradients and slurry aging during the polishing. An aqueous fluorescent solution with matching viscosity is used to model the slurry, a glass window models the wafer and a commercially available polisher provides the polishing pad/table rotating...
MRS Proceedings, 2007
ABSTRACTIt is becoming increasingly clear that understanding the small scale polishing mechanisms... more ABSTRACTIt is becoming increasingly clear that understanding the small scale polishing mechanisms operating during CMP requires knowledge of the nature of the pad-wafer contact. Dual Emission Laser Induced Fluorescence (DELIF) can be used to study the fluid layer profile between the polishing pad and the wafer during CMP. Interactions between the polishing pad surface and the wafer can then be deduced from the fluid layer profile. Previous investigations of pad-wafer interactions using DELIF include in-situ measurements of average fluid layer thickness and asperity layer compressibility, surface roughness measurements and polishing pad rebound into etched wells. In this paper, DELIF is used to determine pad-wafer contact, the point at the fluid film thickness goes to zero. We present a technique and some preliminary data for instantaneous measurement of in-situ pad-wafer contact using DELIF. The imaging area is 1.30×1.74 mm with a resolution of 2.5 μm/pixel. At this magnification, s...
MRS Proceedings, 2004
Duel Emission Laser Induced Fluorescence (DELIF) and friction measurements are taken in-situ duri... more Duel Emission Laser Induced Fluorescence (DELIF) and friction measurements are taken in-situ during CMP to observe slurry flow beneath a model of an integrated circuit (IC) wafer. Friction measurements average around 7.5 lb and multiple frequencies are observed. Slurry film thicknesses on the order of a 10±3μm were observed during CMP of a flat wafer. The film thickness seems uncorrelated to friction measurements except when the pad and wafer rotation speeds are significantly slowed. DELIF has also accurately measured a 9μm etched step, with noise in the image equal to ±3 μm.
World Tribology Congress III, Volume 2, 2005
Modifications to the Dual Emission Laser Induced Fluorescence (DELIF) procedure used to collect i... more Modifications to the Dual Emission Laser Induced Fluorescence (DELIF) procedure used to collect images of the slurry layer between the polishing pad and wafer during Chemical Mechanical Planarization (CMP) have provided a means to attain instantaneous, high spatial resolution images of slurry film thickness. Presented here is a technique to determine the calibration factor that correlates image intensity to slurry film thickness. This presentation will discuss how to determine slurry layer shape near wafer features, pad roughness, and pad compressibility.
Tribology Letters, 2008
To test the accuracy of optically measuring contact, we examined the height distribution histogra... more To test the accuracy of optically measuring contact, we examined the height distribution histogram of a simulated rough surface contacting a smooth surface. We qualified the technique sensitivity as a function of the inverse signal-to-noise ratio having values ranging from 0 to 0.3. An explanation of how the analysis technique can be applied to Dual Emission Laser-Induced Fluorescence (DELIF) measurements is provided.
Journal of Science Education and Technology, 2011
We report results and impressions from a three-day inquiry-based workshop for K-8 teachers, aimed... more We report results and impressions from a three-day inquiry-based workshop for K-8 teachers, aimed at improving their understanding of energy from a science and engineering perspective. Results suggest that the teachers made significant gains in understanding and appreciation of important energy concepts, but their comprehension of some key ideas remained incomplete. The dissipation of energy into thermal energy of the environment proved to be a particularly difficult idea, and one that represents a serious obstacle to understanding the principle of the conservation of energy.
Journal of Engineering Education, 1997
Combining LEGO® Dacta building blocks with LabVIEW TM software produced a highly successful, low-... more Combining LEGO® Dacta building blocks with LabVIEW TM software produced a highly successful, low-cost (less than $500 per station excluding computer) alternative method of teaching engineering through hands-on experimentation. Dubbed LEGO® Data Acquisition and Prototyping System (or LDAPS), this combination of tools provides a highly capable workbench for students, yet brings a new level of creativity and fun into teaching engineering at the college level. In this paper we present the methodology and describe one class where it is currently in use. Student, faculty, and staff response to the class was very positive, partly due to the popularity of hands-on engineering and partly because LEGO® blocks allow the students to exercise their creativity and innovation. The strength in the LDAPS methodology lies in the power of the LEGO® bricks and the LabVIEW TM software. LEGO® motors, sensors, and bricks are almost infinitely configurable, making each experiment unique. LabVIEW TM is a powerful, visual programming language in which students can perform advanced signal processing with relatively few programming skills. We are currently extending this methodology to teach engineering to liberal arts majors as well as precollege students.
Journal of The Electrochemical Society, 2000
In order to better understand the role of the uid behavior in CMP, we measured slurry transport b... more In order to better understand the role of the uid behavior in CMP, we measured slurry transport beneath a glass wafer. We quanti ed the slurry transport using Residence Time Distribution techniques and two measures of slurry transport e ciency de ned as the percentage of new slurry beneath a wafer. Slurry transport e ciency depended on platen speed, ow rate, and the conditioning method. We found that the average uid residence times under the wafer decreased roughly linearly with platen speed. A threefold increase in platen speed decreased slurry mean residence times by three and a half times. Changing the ow rate from 20 cc min to 50 cc min decreased the slurry mean residences by 80. In situ conditioning generally increased the slurry mean residence times and the amount of slurry mixing. In situ conditioning also decreased gradients in the slurry composition across the wafer. Pad topography had a large e ect on the slurry gradients that developed across the wafer. Finally, w e found that the slurry mixing history can be accurately modeled using a simple continuous function.
Journal of The Electrochemical Society, 2005
In situ fluid film pressure and interfacial friction measurements during chemical mechanical plan... more In situ fluid film pressure and interfacial friction measurements during chemical mechanical planarization ͑CMP͒ are reported over a range of applied loads ͑27.6-41.4 kPA or 4-6 psi͒ and relative pad/wafer velocities ͑0.35-0.58 m/s͒. The slurry film pressure beneath contoured test wafers was measured using a novel experimental setup that enables dynamic data collection. The friction data have a repeatability of ϳ10%. The uncertainty of the pressure measurements and the computed down forces were ±2.1 kPa͑±0.3 psi͒ and 20%, respectively. The data indicate that wafer shape, specifically global curvature, is a significant factor in determining the lubrication regime during CMP. Full hydrodynamic lubrication, in which the slurry fluid film supports the entire applied load, was not realized for either concave ͑center high͒ or convex ͑center low͒ wafers. The data for concave wafers show that −6% to 37% of the applied load is supported by the slurry film, where the negative sign indicates suction conditions that were obtained at the lowest applied load condition. CMP of convex wafers is found to operate closer to full hydrodynamic lubrication, with the fluid layer supporting 36% to 64% of the applied downforce. In all cases, the measured friction coefficient decreased as the support of the fluid layer increased ͑higher positive pressures͒. CMP of concave wafers is more sensitive to changes in applied downforce, while the convex wafer type was most affected by changes in the wafer/pad rotation speed, which in turn determines effective slurry film velocity beneath the wafer. Overall, the CMP conditions seen in these scaled experiments operate primarily in the partial lubrication regime shifting closer to hydrodynamic lubrication for convex wafers at the high load, high speed conditions.
Journal of The Electrochemical Society, 2009
The objective of this work is to obtain in situ slurry fluid flow data during the chemical mechan... more The objective of this work is to obtain in situ slurry fluid flow data during the chemical mechanical planarization ͑CMP͒ process. Slurry flow affects the material removal processes, the creation of defects, and consumable use during CMP, and therefore impacts the cost and quality of polishing. Wafer-scale flow visualization using seeded slurry was accomplished for a variable applied load ͑0.3-2.5 psi downforce͒, wafer rotation speed ͑0 and 33 rpm͒, slurry injection locations, and various pad types ͑flat, XY grooved, and AC grooved͒. In situ pad conditioning was employed in all experiments. The data indicated complex slurry flow fields on the pad surface in the wafer vicinity, which are influenced by slurry injection point, pad grooving, downforce, and wafer/conditioner rotation. Injection location and pad type were shown to have the strongest impact on the variation in the fluid flow fields obtained.
Journal of The Electrochemical Society, 2004
Chemical mechanical planarization ͑CMP͒ is a process widely used for the manufacture of silicon i... more Chemical mechanical planarization ͑CMP͒ is a process widely used for the manufacture of silicon integrated circuits. In this work, we measured the thickness of the slurry film between the wafer and the pad during polish while simultaneously measuring the frictional drag. All experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer downforce control. Dual emission laser-induced fluorescence techniques optically measured the slurry film thickness through a dual-camera imaging system. The resulting data are discussed for wafers polished with a 3.1 wt % abrasive concentration slurry solution on Freudenberg's FX-9 polishing pads. It was found that the degree of surface curvature of the wafer substrate significantly influences the slurry film thickness and wafer drag, and therefore, the polish. The convex wafer shows the expected behavior of increased downforce reduces the slurry film thickness and increases the coefficient of friction. Further, as the pad speeds up, the slurry thickness increases and the friction decreases. The concave wafer shows no change in slurry film thickness and a decrease in the frictional coefficient with increasing downforce. Both the film thickness and frictional coefficient appear to decrease slightly with increasing pad speed. This difference between the two wafer shapes reflects the different fluid mechanics in each case.
Journal of The Electrochemical Society, 2009
Achieving device-and wafer-scale planarity in integrated circuit manufacturing is increasingly ch... more Achieving device-and wafer-scale planarity in integrated circuit manufacturing is increasingly challenging as device sizes are reduced to 35 nm and smaller, and wafer sizes are increased from 300 to 450 mm. Hence a better understanding of chemical mechanical planarization ͑CMP͒ processes is needed. We report the synchronous, in situ measurement of wafer forces ͓coefficient of friction ͑CoF͔͒ and wafer orientation during CMP polishing of BK7 glass wafers and the ex situ measurement of material removal rate ͑MRR͒ over a wide range of applied vertical loads and relative rotational velocities. MRR appears to be Prestonian and was significantly reduced by moving the slurry injection location to the outer edge of the wafer track leading to slurry starvation. Both positive and negative wafer pitch angles were measured, indicating that apparently contradictory modeling reports in the literature may not be in conflict. A phenomenological linkage between wafer orientation and frictional behavior was observed with positive pitch angles ͑from +0.2 to +0.4°͒ corresponding to smooth polishing and nose-down angles ͑from −0.2 to +0.2°͒ corresponding to stick-slip. Spectral signal analysis shows that the variation of CoF is due to platen rotation effects, while wafer orientation variation is affected by both platen and wafer rotations.
Experiments in Fluids, 2011
Dual emission laser induced fluorescence (DELIF) is a technique for measuring the instantaneous t... more Dual emission laser induced fluorescence (DELIF) is a technique for measuring the instantaneous thin fluid film thickness in dynamic systems. Two fluorophores within the system produce laser induced emissions that are filtered and captured by two cameras. The ratio of the images from these cameras is used to cancel the effect of the laser beam profile on the image intensity. The resultant intensity ratio can be calibrated to a fluid film thickness. The utilization of a 2-dye system when applied to Chemical Mechanical Polishing (CMP) is complicated by the fluorescence of the polymeric polishing pad and the light scattering particles in the polishing slurry. We have developed a model of DELIF for CMP with 1-dye employing the polishing pad as the second fluorophore. While scattering particles in the slurry decrease the overall intensity of the individual images, the contrast in the image ratio increases. Using the 1-dye DELIF system to measure thin slurry films, our model results indicate that a cubic calibration may be needed. However, experimental results suggest a linear calibration is achieved for slurry films between 0 and 133 lm thick with scattering coefficients as high as 8.66 mm-1 at a wavelength equal to 410 nm.
Electrochemical and Solid-State Letters, 2005
Recent experimental advances using Dual Emission Laser Induced Fluorescence (DELIF) and image pro... more Recent experimental advances using Dual Emission Laser Induced Fluorescence (DELIF) and image processing have provided high spatial and temporal resolution maps of the slurry layer during Chemical Mechanical Polishing (CMP). Intensity differences in the images correspond to fluid layer thickness variations as the slurry passes between different pad and wafer topographies. Asperities expand under 14µm deep wells and are compressed beyond the trailing edge of the well. Air pockets travel from the leading to the trailing edge of the wafer through 27µm deep wells. The pads tested were Freudenberg FX9, Rodel IC1000, and experimental pads from Cabot Microelectronics.
Electrochemical and Solid-State Letters, 2010
As semiconductor device sizes continue to shrink and economic realities drive ever increasing yie... more As semiconductor device sizes continue to shrink and economic realities drive ever increasing yield targets, achieving wafer scale planarity through the application of chemical mechanical planarization ͑CMP͒ has become increasingly challenging. The dynamics of the wafer-pad interface is critical to maintaining this uniformity. Utilizing measured friction coefficients ͑0.3-0.6͒, we report on the transitions from a smooth planarization regime to a stick-slip regime and vice versa over a set of two applied vertical loads and three relative velocities during the CMP process. Finally, we note a correlation between time spent in a stick-slip regime and platen velocity.
Micromachined structures with diameters ranging from 50-100 µm have been applied to the measureme... more Micromachined structures with diameters ranging from 50-100 µm have been applied to the measurement of the microscale shearing forces present at the wafer-pad interface during chemical mechanical polishing (CMP). The structures are 80 µm high poly-dimethyl-siloxane posts with bending stiffnesses ranging from 1.6 to 14 µN/µm. The structures were polished using a stiff, ungrooved pad and 3 wt% fumed silica slurry at relative velocities of approximately 0.5 m/s and downforces of approximately 1 psi. ...