Advanced Silicon Processing & Manufacturing Techniques

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MODULE PROFILE

Module Number: 11

Title: Lithography

Delivered by: University of Edinburgh

Module Credits: 15

Assessment Weighting:

  • Pre-residential work: 3
  • Post-residential work: 7
  • Examination: 10

Convenor:

  • Dr J Tom M Stevenson, University of Edinburgh

Lecturers:
Internal:

  • Professor Anthony J Walton
  • Dr J Tom M Stevenson
  • Mr Alan Ross

Industrial:

  • Dr Chris Mack, KLA-Tencor, USA
  • Dr Frank Linskens, Rohm & Haas Electronic Materials, USA
  • Dr Kevin Lucas, Motorola, Crolles - France
  • Professor Ron A Lawes, RAL - CMF
  • Dr Andrew Hourd, Compugraphics, Glenrothes
  • Mr Martin McCallum, Nikon, Livingston

Industrial Advisors:

  • Dr Andrew Hourd Compugraphics, Glenrothes
  • Mr Keith Chivers, Nikon, Livingston

Aims:

The aim of this module is introduce the science, technology, engineering and applications of lithography in the manufacture of integrated circuits. It includes an overview of the role of lithography in the wider field of process development.

Learning Objectives:

On successful completion of this module, delegates will have gained an understanding of:

  • the basic requirements of the lithographic process, photoresist materials, optical exposure tools and mask making in relation to process evolution and CD trends
  • the mechanism of image formation in optical systems, the effects of diffraction, the limits of lens performance and the relationship between the aerial image and the profile of the resist after development
  • image problems posed during multi-layer processing, the optimisation of exposure/focus, the design of alignment systems and sources of overlay error
  • the reasons for moving to shorter wavelength, the design of equipment, materials and techniques for DUV lithography
  • the alternatives to optical lithography and the likely options for future generations of integrated circuits, with reference to the SIA roadmap

Assessment:

  • Pre-residential sessions: assignments 15 %
  • Post-residential sessions: assignments 35 %
  • Examination (supervised) 50 %

Background to the Module:

Lithography is a strategic technology in the manufacture of integrated circuits, accounting for about 25% of overall process costs. Technical developments in lithography have enabled packing densities to increase, whilst maintaining yield, in processes where the complexity and the number of layers is steadily rising. A modern CMOS process may have 20 - 25 lithography steps with deep sub-micron geometries on the critical layers.

The technical content of this module compliments many of the other modules, but is particularly relevant to Module 12 (Etch) and Module 4 (Interconnect & Metallisation).

Pre-Requisite Knowledge

Delegates will be expected to have knowledge of physics to degree level and some experience of IC fabrication. Prior experience in lithography is desirable but not necessary.

Delivery & Assignments

A study pack will be sent to delegates before the start of the module.

  • Pre-residential sessions:
    • directed reading
    • problem solving/exercises
  • Residential week:
    • lectures
    • laboratory demonstrations
    • simulation workshops
    • tutorials/case studies

Laboratory sessions are an important component of this course which will give delegates the opportunity to be involved with the practical elements of the lithographic process. In addition there will be laboratories where students will be introduced to the simulation of lithography processes. This will use the extensive base of Unix workstations within the Department of Electronic and Electrical Engineering.

Post-Course Work

Delegates will be set work to complete after the conclusion of the residential week, which will make extensive use of the information presented and facilitate an assessment of their understanding.

  • advanced problem solving
  • written report (2000 to 4000 words)
  • supervised examination (3 questions from 5, 2 hours)

SYLLABUS

  • Lectures 24 hours
  • Laboratory sessions 7 hours
  • Case studies/Tutorials 2 hours
Time
Topic Content
Day 1
Basic requirements of the lithography process: photoresist materials, optical exposure tools and maskmaking.
  • SIA Roadmap: process evolution and CD trends
  • CD and overlay demands on the lithographic process
  • evolution of optical lithography
    - contact/proximity
    - scanning projection
    - wafer steppers
    - step & scan
  • novolac photoresist materials - basic chemistry
    - exposure mechanism
    - developer action
    - sensitivity, contrast
  • generic optical projection aligner
    - illuminator
    - objective
    - alignment system
  • maskmaking for deep sub-micron lithography (GS)
DAY 2
Image formation in optical systems: the effects of diffraction, the limits of lens performance and the relationship between the aerial image and the profile of the resist after development.
  • basic theory of diffraction diffraction gratings/diffracted orders
  • lens performance
    - numerical aperture
    - resolution
    - partial coherence
    - depth of focus
    - distortion
    - aberrations
  • simulation of aerial images
    - input parameters
    - intensity profile in image
    - exposure threshold
    - resist contrast
  • developed resist profiles
    - development models
    - key parameters
    - developed profile
  • defect inspection and metrology (GS)
DAY 3
Imaging problems posed during multi- layer processing: the optimisation of exposure and focus, the design of alignment systems and sources of overlay error.
  • reflections from substrate layers
  • energy coupled into resist film
  • anti-reflection coatings
  • optimisation of exposure/focus
    - CD tolerances
    - CD metrology methods
    - E/D curves
  • visibility of alignment marks
    - alignment strategy
    - resist flow over marks
    - thickness variations
    - planarisation
  • analysis of overlay error
    - capture of marks
    - wafer distortion
    - image distortion
    - stage errors
    - overlay metrology
  • optical lithography equipment
    - future trends (GS)
DAY 4
Short wavelength systems: aspects of the design of equipment, materials and techniques for DUV lithography.
  • advantages of shorter wavelength
  • sources of illumination
    - excimer lasers
  • DUV imaging systems
    - illuminator design
    - exposure uniformity
    - lens materials
    - lens design
    - alignment systems
  • DUV photoresist materials
    - basic chemistry
    - exposure mechanism
    - chemical amplification
    - PEB requirements
    - sensitivity, contrast
  • anti-reflection coatings for DUV
  • demonstration of DUV lithography at 0.18um (at Nikon, Livingston)
DAY 5
Alternatives to optical lithography: e-beam systems and lithography options for future generations
  • alternatives to optical lithography (GS)
  • e-beam exposure systems
    - electron guns (sources)
    - column design
    - deflector systems
    - scan linearity
    - XY stage design
    - alignment/overlay
    - age/data processing
  • resists for e-beam exposure
    - sensitivity
    - dose/scatter
    - contrast
    - development
    - etch resistance
  • demonstration of e-beam lithography at sub 0.1um
  • SIA roadmap re-visited
  • future lithography techniques

Recommended Texts

(in order of preference)

No single book covers this subject in the depth and breadth required. However, the following books give a reasonable background and cover some of the course material.

  • P. Rai-Choudhury, "Handbook of Microlithography, Micromachining and Microfabrication", Volume 1 - Microlithography, Co-published by SPIE and IEE 1997.
    ISBN 0-8194-2378-5. This is the main book for the module
  • S.A. Campbell, "The Science and Engineering of Microelectronic Fabrication", Oxford University Press, 1996.
    ISBN 0-19-510508-7
  • D.J. Elliott, "Integrated Circuit Fabrication Technology", McGraw Hill, 1989. ISBN 0-07-019339-8
  • James R. Sheats & Bruce W. Smith, "Microlithography - Science and Technology", Dekker 1998. ISBN 0-8247-9953-4

Conference & Journal Papers

SPIE Conference Proceedings are an excellent source of material. (e.g. Proc: SPIE vol: 3334 Optical Microlithography XI Feb: 1998). The SPIE Website is ' http://www.spie.org'.

TIMETABLE

NB: Details of module content, timetable and lecturers may be subject to change

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Module 11

 

   
Time
Monday
Tuesday
Wednesday
Thursday
Friday
09.00 - 10.30
Introduction, SIA roadmap: Implications for lithography
Imaging on real substrates: some of the problems
Metrology
A Process Overview
Tour of SMC Cleanrooms
Alignment Systems
and Sources of
Overlay Error
10.30 - 11.00
COFFEE
COFFEE
COFFEE
COFFEE
COFFEE
11.00 - 12.30
Optics for Projection Overlay
Introduction to Optical Proximity Correction
Introduction to Lithography Modelling (I)
Iimaging Systems
Optical Lithography Equipment: Future Trends
12.30 - 13.30
LUNCH
LUNCH
LUNCH
LUNCH
LUNCH
13.30 - 15.00
Novolac/DNQ Photoresist Chemistry & Processing
Overview of the Alternatives to Optical Lithography
Lithography Modelling (2)
Mask-making for Deep Sub-micron Lithography
ITRS Road Map
re-visited:
The Way Forward
15.00 - 15.30
TEA
TEA
TEA
TEA
TEA
15.30 - 17.00
Chemically Amplified Resists: Chemistry & Processing
Electron-Beam Exposure Systems & Resists
Lithography Modelling
(3) and (4)
Demonstration of Lithography

Course Review Discussion
Course Ends

     
COURSE BANQUET
Enquiries and further information from:

Mrs Sandra Peace
IGDS Programme Co-ordinator,
IGDS Office
School of Electronics & Physical Sciences
University of Surrey
Guildford
Surrey
GU2 7XH UK

Tel +44 (0)1483 686 138
Fax +44 (0)1483 686 139
e-mail: s.peace@surrey.ac.uk
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