BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//TU/e ME//Events//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:Europe/Amsterdam
BEGIN:STANDARD
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
UID:event-27@tuemeche.nl
DTSTAMP:20261007T234735Z
DTSTART;TZID=Europe/Amsterdam:20261102T160000
DTEND;TZID=Europe/Amsterdam:20261102T173000
SUMMARY:A deformable wafer table for semiconductor lithography
DESCRIPTION:Speaker: Sander Hermanussen\nHost: Hans Vermeulen\n\nFor the 
 past decades\, the semiconductor industry has mainly focused on decreasin
 g the feature size on inte-grated circuits. The number of transistors tha
 t can be fitted on an integrated circuit doubles roughly every 18-24 mont
 hs\, referred to as Moore's law. By using state-of-the-art extreme ultrav
 iolet (EUV) photolithog-raphy machines\, the achievable critical dimensio
 n (e.g.\, gate length or linewidth) on integrated circuits is currently a
 pproximately 10-20nm. As the demand for efficient computing power is expe
 cted to continue to grow\, and further 2D miniaturization becoming increa
 singly challenging\, the semiconductor industry is now looking to vertica
 l integration: effectively stacking more functional layers to build up a 
 3D integrated circuit.\nThis places new requirements on photolithography 
 machines. In these systems\, thin silicon substrates\, called wafers\, ar
 e exposed with ultraviolet light to create the features that make up an i
 ntegrated circuit. The deposition and processing of preceding layers cumu
 latively introduce stress into the wafer. The resulting deformations can 
 accumulate to over a millimeter of out-of-plane warpage of the wafer. Whe
 n clamping a warped wafer on a wafer table\, these out-of-plane deformati
 ons lead to in-plane deformations\, due to fric-tion and slip between the
  wafer and wafer table\, as well as the resulting wear of the wafer table
 . This leads to misalignment between consecutive layers\, known as overla
 y errors.\nTo address these issues\, a conceptual design for a piezoelect
 ric deformable wafer table is presented. Two applications are identified.
  First\, to mitigate the effects of clamping a highly warped wafer onto a
  flat wafer table\, the concept of conformal wafer loading is introduced.
  To minimize slip between the wafer and wafer table during wafer load\, t
 he wafer table is actuated conformal to the wafer\, prior to clamping the
  wafer. By actuating the wafer table along the neutral bending plane of t
 he wafer\, the wafer can be flattened without introducing relative motion
  between the wafer and wafer table. Secondly\, overlay and focus errors c
 an be reduced using intra-field corrections. During exposure\, the wafer 
 can be locally deformed to match the aerial image projected by the optica
 l system\, which compensates for both remaining deformations in the wafer
 \, as well as optical aberrations.\nA design for a deformable wafer table
  is presented based on a multilayered piezoelectric actuator\, on top of 
 which a glass-ceramic wafer clamp is placed. For both conformal wafer loa
 ding and intra-field corrections\, it is necessary to independently actua
 te in-plane strain across two orthogonal axes\, in-plane shear strain\, c
 ur-vature across two orthogonal axes\, and finally a twisting curvature. 
 This is accomplished by stacking six pie-zoelectric layers\, each of whic
 h can generate piezoelectric strain in a specific in-plane direction. Two
  embod-iments are analyzed: first\, a design based on monolithically sint
 ering ceramic lead-zirconate-titanate (PZT)\, to which an in-plane electr
 ic field can be applied using embedded interdigitated electrodes (IDEs)\;
  secondly\, a design based on stacked monocrystalline lithium niobate (LN
 ) wafers with planar electrodes\, where the in-plane strain is obtained t
 hrough a favorable crystal orientation.\nKey aspects of this design such 
 as the layer thickness\, electrode dimensions\, and material orientation 
 are optimized using a lightweight mathematical plate model. By combining 
 this model with a finite element unit cell simulation\, the microscopic d
 eformations around the interdigitated electrodes could be scaled to the m
 acroscopic deformation of the deformable wafer table. Using this method\,
  the PZT and LN concepts were compared\, and found to yield similar perfo
 rmance. While PZT has a higher piezoelectric coefficient\, the ma-terial 
 away from the IDEs does not efficiently contribute to generating strain. 
 The low piezoelectric coeffi-cient of LN is largely compensated by the mu
 ch higher coercive field\, and all material between the planar electrodes
  is efficiently used.\nBy splitting the wafer table actuator into segment
 s\, actuation at higher spatial frequencies is facilitated. This will inc
 rease both the conformal wafer loading performance\, by reducing the mism
 atch between wafer and wafer table shape\, as well as the intra-field cor
 rection performance by enabling higher-order corrections. The actuator in
 fluence functions of the segments are calculated using a finite element m
 odel\, leveraging shell elements for computational efficiency. To charact
 erize the different segmentations\, two methods are pre-sented. The first
  is based on using an intermediate orthogonal decomposition of the soluti
 on space\, and evaluating how well the actuator system can approximate th
 e most relevant modes from this decomposi-tion. For this method\, Zernike
  and Legendre polynomials are used for evaluating conformal wafer loading
  and intra-field corrections respectively. The second method is based on 
 taking the singular value decomposi-tion of the reachable actuator space\
 , and optionally combining the associated singular values into a perfor-m
 ance measure. For the requirements set in this thesis\, a 61-element hexa
 gonal segmentation resulted in a good balance between performance and com
 plexity.\nFor both the PZT- and the LN-based design\, a prototype was dev
 eloped. For the PZT concept\, multiple itera-tions were produced\, based 
 on tape casting PZT sheets and screen printing the interdigitated electro
 des\, followed by binder burnout\, sintering and poling. However\, the bi
 nder burnout proved difficult to control\, resulting in repeated failures
 . It is hypothesized that a better process control of the tape casting an
 d screen printing could improve the probability of success. Next\, an LN-
 based prototype was produced using com-mercially available off-the-shelf 
 LN wafers\, with sputtered electrodes connected through brass foil spacer
 s. This prototype demonstrated the feasibility of independently actuating
  curvature and in-plane strain\, as well as achieving large deformations 
 using the presented actuator concept.\nIn conclusion\, a design for a def
 ormable wafer table was presented\, which enables both conformal wafer lo
 ading and intra-field corrections. By stacking six piezoelectric layers\,
  three in-plane strain and three curva-ture components can be independent
 ly actuated. Two types of piezoelectric layers were investigated\, and th
 eir dimensions optimized for maximum curvature. First\, ceramic lead-zirc
 onate-titanate (PZT) can be sin-tered with embedded interdigitated electr
 odes which are used for both poling and actuating the layers. Sec-ondly\,
  monocrystalline lithium niobate (LN) wafers can be stacked\, separated b
 y planar electrodes to actuate the layers. Although PZT has a high piezoe
 lectric coefficient\, the material is utilized less efficiently with the 
 interdigitated electrodes\, and manufacturing a prototype proved very dif
 ficult. In contrast\, the crystal orien-tation of LN can be tuned for max
 imal performance\, and the actuator concept was proven with a prototype m
 ade from commercially available LN wafers. To increase the spatial resolu
 tion of the deformable wafer table\, a segmented design was analyzed\, wi
 th a hexagonal 61-element segmentation providing an optimal balance betwe
 en complexity and performance.\n\nMore info: https://research.tue.nl/nl/p
 ersons/sander-j-hermanussen/
LOCATION:Atlas 0.710
URL:https://tuemeche.nl/peoplepages/event.php?id=27
CATEGORIES:PhD Defense
END:VEVENT
END:VCALENDAR