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 2004

21st 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: www.binnard.com/SJSUlitho.ppt

ME-250 Fall 2004

_________________________________________________________________________________________________________________

Source: www.uspto.gov (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 tool10 – Linear Motor66 – Wafer Table68 – Wafer72 – Metrology Frame74 – Illumination Assembly76 – Reticle78 – Lens80 – Photomask102 – Wafer Stage Base104 – Wafer Table106 – Flexures112 - Encoders122 – Vibration Isolators 124 – Vibration Isolators126 – Air Bearings201 – AF/AL Emitter202 – AF/AL Receiver203 – 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: www.uspto.gov (US Patent # 6,686,991)

ME-250 Fall 2004

______________________________________________________________________________________________________________________

Source: www.uspto.gov (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: www.uspto.gov (US Patent # 5,757,160)

Components of the wafer stage assembly

10 – Wafer Stage11 – Right handed Cartesian coordinate system12 – Wafer14 & 16 – Laser Gauge Type Interferometers22 & 24 – Penta Prism Beam Splitter26, 28 & 38 – Beam Folder/Fold Mirror34 – Laser37 – Beam of light40 – Wavelength Monitor30 & 32 – Two Orthogonal Reference Mirrors35 - 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: www.uspto.gov (US Patent # 5,757,160)

ME-250 Fall 2004

Moving Interferometer Wafer Stage (Perspective View)

________________________________________________________________________________________________________________________________Source: www.uspto.gov (US Patent # 5,757,160)

Components of the wafer stage assembly

12 – Wafer Chuck14 & 16 – Laser Gauge Type Interferometers22 & 24 – Penta Prism Beam Splitter30 & 32 – Two Orthogonal Reference Mirrors34 – Laser37 – Beam of light42 – Air Bearing in triangular arrangement44, 46, 48 & 52 – Beam Folder/Fold Mirror54 - Arm56 – Reference Mirror58 – Counter Force Cylinder60 – Support 62 – Liner Drive/ Motor 64 - Travel of wafer table in X-Direction66 – 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: www.uspto.gov (US Patent # 5,757,160)

ME-250 Fall 2004

Precision Concepts In Interference Lithography

_______________________________________________________________________________________________________________________Source: http://snl.mit.edu/papers/presentations/2003/Schattenburg/Schattenburg-DARPA-2003.pdf

ME-250 Fall 2004

References

1) Precision Engineering in Semiconductor Lithography, Binnard M., Nikon Reaserch Incorporation of America, Oct 5, 2004.

www.binnard.com/SJSUlitho.ppt

2) Wafer stage assembly, servo control system, and method for operating the same, Binnard, et al., US patent # 6,686,991, Feb 3, 2004.

http://patft.uspto.gov/netahtml/srchnum.htm

3) Moving interferometer wafer stage, Kreuzer, US patent # 5,757,160, May 26, 1998.

http://patft.uspto.gov/netahtml/srchnum.htm

4) 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, 2003.http://snl.mit.edu/papers/presentations/2003/Schattenburg/Schattenburg-DARPA-2003.pdf