ME-250 Precision Machine Design Semiconductor Lithography Tool Alok Bhatt Sarang Deshpande Instructor: Dr. B. J. Furman Mechanical and Aerospace Engineering Department San Jose State University Fall st Oct 2004

ME-250 Fall 2004 Overview  Traditional lithography tool  Precision aspects involved  Concept of HTM  Moving interferometer wafer stage  Precision aspects involved  Precision concepts in interference lithography  References

ME-250 Fall 2004 Schematic of Photolithography Tool ___________________________________________________________________________________________________________ Source:

ME-250 Fall 2004 _________________________________________________________________________________________________________________ Source: (US Patent # 6,686,991) Reticle Stage Lens Wafer Stage Voice coil Motor 2X Schematic Diagram of Photolithography Tool Linear Motor 2X Components of the lithography tool 10 – Linear Motor 66 – Wafer Table 68 – Wafer 72 – Metrology Frame 74 – Illumination Assembly 76 – Reticle 78 – Lens 80 – Photomask 102 – Wafer Stage Base 104 – Wafer Table 106 – Flexures Encoders 122 – Vibration Isolators 124 – Vibration Isolators 126 – Air Bearings 201 – AF/AL Emitter 202 – AF/AL Receiver 203 – Voice coil Motor x z Y

ME-250 Fall 2004 Precision Engineering Principles Involved Vibration Isolators Flexures Encoders Air Bearings Two linear motors provide motion to wafer stage in Y-axis. Plurality of motors eliminates Abbe Error Three voice coil motors for positioning the wafer table relative to wafer stage in Z-axis Two flexures to restrict the planner motion of the wafer table in X and Y axis, while allowing its motion in Z-direction Vibration isolators to resist the vibrations to transfer from base to wafer stage Air bearings are used between wafer stage and wafer base. A thinner layer of pressurized air is applied while vacuum holds the stage in position AF/AL (Auto Focus/ Auto Level) sensors provide the position of exposure point relative to the wafer Plurality of encoders (112) determines the position of wafer table relative to wafer stage ___________________________________________________________________________________________________________ Source: (US Patent # 6,686,991)

ME-250 Fall 2004 ______________________________________________________________________________________________________________________ Source: (US Patent # 6,686,991) Concept of HTM Utilized In Positioning of Wafer Stage “r” are position vectors “R” are the coordinate rotations Coordinate Frame “O” is reference coordinate system “O1” is coordinate frame for wafer stage “O2” is coordinate frame for wafer stage base “O3” is coordinate frame for wafer table “O4” is coordinate frame for lens Six different encoders determine position of each coordinate system and put them into a matrix form Position of each coordinate system relative to the reference coordinate system is then determined by homogeneous transformation matrices (HTM)

ME-250 Fall 2004 Moving Interferometer Wafer Stage (Vertically Mounted) ____________________________________________________________ Source: (US Patent # 5,757,160) Components of the wafer stage assembly 10 – Wafer Stage 11 – Right handed Cartesian coordinate system 12 – Wafer 14 & 16 – Laser Gauge Type Interferometers 22 & 24 – Penta Prism Beam Splitter 26, 28 & 38 – Beam Folder/Fold Mirror 34 – Laser 37 – Beam of light 40 – Wavelength Monitor 30 & 32 – Two Orthogonal Reference Mirrors 35 - Travel of Mirror in X-Direction Present Invention of Moving Interferometer Wafer stage

ME-250 Fall 2004 Distinct Features: The wafer stage typically has 3 DOF Interferometers move with wafer stage Two stationary orthogaonal return interferometer mirrors for accurate alignment and positioning, placed off the moving stage Objectives: To reduce the errors in positioning and alignment To reduce the size and weight / to increase the travel distance Advantages: Lower power laser illumination source can be used It is more tolerant of rotation or twisting of the wafer stage Elimination of Abbe Offset error by mounting the interferometers in or close to the wafer plane Moving Interferometer Wafer Stage (Vertically Mounted) ____________________________________________________________ Source: (US Patent # 5,757,160)

ME-250 Fall 2004 Moving Interferometer Wafer Stage (Perspective View) ________________________________________________________________________________________________________________________________ Source: (US Patent # 5,757,160) Components of the wafer stage assembly 12 – Wafer Chuck 14 & 16 – Laser Gauge Type Interferometers 22 & 24 – Penta Prism Beam Splitter 30 & 32 – Two Orthogonal Reference Mirrors 34 – Laser 37 – Beam of light 42 – Air Bearing in triangular arrangement 44, 46, 48 & 52 – Beam Folder/Fold Mirror 54 - Arm 56 – Reference Mirror 58 – Counter Force Cylinder 60 – Support 62 – Liner Drive/ Motor 64 - Travel of wafer table in X-Direction 66 – Calibration Detector

ME-250 Fall 2004 Precision Engineering Principles Involved Elimination of Abbe Offset error by mounting the interferometers in or close to the wafer plane The wafer stage rides on three air bearings placed in a triangular arrangement which is an example of a kinematically mounted wafer stage By placing the mirrors off the wafer stage, the mirrors can be made lager, more stable and can be manufactured more accurately at lower cost The wafer stage can be made smaller and of less weight Wafer stage rotation accuracy is also improved by increasing the separation of the paired interferometers without increasing the size of the wafer stage ________________________________________________________________________________________________________________________________ Source: (US Patent # 5,757,160)

ME-250 Fall 2004 Precision Concepts In Interference Lithography _______________________________________________________________________________________________________________________ Source:

ME-250 Fall 2004 References 1) Precision Engineering in Semiconductor Lithography, Binnard M., Nikon Reaserch Incorporation of America, Oct 5, ) Wafer stage assembly, servo control system, and method for operating the same, Binnard, et al., US patent # 6,686,991, Feb 3, ) Moving interferometer wafer stage, Kreuzer, US patent # 5,757,160, May 26, ) Nano-metrology using the Nanoruler, M.L. Schattenburg, P. Konkola, C. Chen, R.K. Heilmann, C. Joo, J. Montoya and C.-H. Chang, Defense Advanced Research Projects Agency (DARPA) - Advanced Lithography Program Review, Santa Fe, New Mexico, May 5-8, pdf pdf