Impact of Litho on Design

Transcription

1 Impact of Litho on Design Srini Raghvendra Senior Director DFM Solutions Synopsys Inc.

2 Acknowledgements Dan Page Mike Rieger Paul vanadrichem Jeff Mayhew 2006 Synopsys, Inc. (2)

3 Subwavelength Litho Requires Designer Involvement 10 Above Wavelength SubWavelength 3.0µm 2.0µm nm 1.0µm 0.6µm 365nm 0.35µm 0.25µm 248nm 193nm 193nm immersion 157nm 0.1 Silicon Feature Size Lithography Wavelength 0.18µm 0.13µm 90nm 65nm 45nm 32nm Synopsys, Inc. (3)

4 5 Reasons Litho Matters to the Designer 1. CMP Metal fill 2. OPC 3. PSM 4. Assist Features 5. Off Axis Illumination 2006 Synopsys, Inc. (4)

5 CMP Impacts Litho Imaging related!! Mask No OPC Too high!! Ideal stack height Too low!! Large solid area TILES Isolated Line Dense Metal 2006 Synopsys, Inc. (5)

6 OPC 2006 Synopsys, Inc. (6)

7 Corner-Intensive Geometries such as Notches are Hard to Correct and Manufacture Bad: Too many corners at minimum width Good: Less corners and wider wire Better: Minimum number of corners Best : Minimum number of corners and non-minimum width wires 2006 Synopsys, Inc. (7)

8 Router Should Prevent Litho Unfriendly Patterns Minimum jog length Minimum edge length 2006 Synopsys, Inc. (8)

9 Assist Features 2006 Synopsys, Inc. (9)

10 CD versus pitch problem Line width* 65nm line on reticle Pitch nm on wafer Forbidden pitch pitch (AU) Poly line width variation has direct impact on drain current *litho term: Critical Dimension (CD) 2006 Synopsys, Inc. (10)

11 How to compensate CD vs pitch Assist features ROPC MOPC Sub 130nm: Assists + MOPC 2006 Synopsys, Inc. (11)

12 Assist features may give you another unwanted pitch X? OK No room to place an effective assist feature OK Optimum assist feature locations too close together OK 2006 Synopsys, Inc. (12)

13 PSM 2006 Synopsys, Inc. (13)

14 Attenuated-Phase Shifting Mask Technology Also called half-tone, Att-PSM, weak-psm, leaky-chrome, etc. Uses weak phasemodulation at the mask level to further the resolution capabilities of optical lithography Benefits: Simpler design-flow issues than Alt-PSM Lower cost than Alt-PSM Chrome Att-PSM Mask 180 Mask Light intensity of binary mask EM Resulting field of light Att. intensity PSM of Att. PSM Difficulties: Not as beneficial as Alt-PSM Spurious sidelobes demand advanced verification 2006 Synopsys, Inc. (14)

15 E-PSM Used Often with Contacts Contact mask pattern Contacts printed on wafer Exposure intensity distribution on wafer Unwanted Artifacts printed on wafer by constructive interference of sidelobes 1 micron Some arrangements of via placements can cause unwanted features to print: forbidden 2D pitches 2006 Synopsys, Inc. (15)

16 Phase Shifting: Enabling Technology Uses phase-modulation at the mask level to further the resolution capabilities of optical lithography Mask 180 o phase-shifter Benefits: Smaller feature sizes Improved yield (tighter process control) Resolution boost!! Light intensity of PSM Light intensity of binary mask EM field of Alt. PSM 0.11µm Printed using a 0.25 µm nominal process 2006 Synopsys, Inc. (16)

17 What is phase coloring poly active Assigning 0 and 180 deg (π) shifters gate 0-shifter π-shifter 2006 Synopsys, Inc. (17)

18 APSM Design layout compliance π 0 π 0 π 0 π? 0 Conflict Layouts for PSM must avoid cyclic conflicts where phases cannot be mapped. PSM feature-dependent minimum space rules must be followed. 45 deg: makes shifter placements too complicated 2006 Synopsys, Inc. (18)

19 Off Axis Illumination Techniques 2006 Synopsys, Inc. (19)

20 Dual Dipole σ in α σ out dipoley Extreme form of Off Axis Dual mask approach Decomposition of data required Comparable with Alt-PSM Logical solution for memory makers Used single dipole Often combines with dipole No 45 deg allowed!! dipolex 2006 Synopsys, Inc. (20)

21 Dual Dipole decomposition dipoley Design dipolex Protection boxes Result on the wafer dipolex exposure dipoley exposure 2006 Synopsys, Inc. (21)

22 Consequences of Double Dipole Work in progress, perhaps rules to make decomposition easier. 45 degree or non-manhattan in general will be very problematic Synopsys, Inc. (22)

23 How Can the Designer Help? 2006 Synopsys, Inc. (23)

24 Litho Compliance Checking Will be Critical at sub-65nm 2006 Synopsys, Inc. (24)

25 Model-based design verification can identify problem configurations Sidelobes CD on 45 line too small Bad space/width combinations 2006 Synopsys, Inc. (25)

26 Design Driven RET Could Improve Manufacturability DRC compliant with margin 2 improve CD uniformity Original DRC-clean design layout minimum clearance contact 1 Widen pad Shift lines improve contact overlay margin Reduce OPC complexity improve clearances 2006 Synopsys, Inc. (26)

27 Summary 2006 Synopsys, Inc. (27)

28 Design Layout Impacts Litho Litho Techniques Impose Restrictions CMP, OPC, PSM, AF, Off Axis Illumination Designers should be aware, and can even help Litho Compliance Checking Will become an important part of sign-off Design Driven RET could be an important aid to manufacturability Synopsys, Inc. (28)

29 Thank You! 2006 Synopsys, Inc. (29)