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Multi-Project Reticle Design & Wafer Dicing under Uncertain Demand PowerPoint PPT Presentation


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Multi-Project Reticle Design & Wafer Dicing under Uncertain Demand. Andrew B Kahng , UC San Diego Ion Mandoiu , University of Connecticut Xu Xu , UC San Diego Alex Zelikovsky, Georgia State University. Multi-Project Wafer s. Mask set cost: >$1M for 90 nm technology

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Multi-Project Reticle Design & Wafer Dicing under Uncertain Demand

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Multi project reticle design wafer dicing under uncertain demand

Multi-Project

Reticle Design & Wafer Dicing under Uncertain Demand

Andrew B Kahng, UC San Diego

Ion Mandoiu, University of Connecticut

Xu Xu, UC San Diego

Alex Zelikovsky, Georgia State University


Multi project reticle design wafer dicing under uncertain demand

Multi-Project Wafers

  • Mask set cost: >$1M for 90 nm technology

  • Share cost of mask tooling between multiple designs!

    • Prototyping

    • Low volume production

Images courtesy of EuroPractice and CMP


Multi project reticle design wafer dicing under uncertain demand

Design Flow for MPW

Die Sizes + Production Volumes

Project Partitioning

Project Cloning

Reticle Floorplaning

Shotmap Definition

Dicing Plan Definition

Reticle, Wafer Shotmap, Wafer Dicing Plans


Multi project reticle design wafer dicing under uncertain demand

Design Flow for MPW

Die Sizes + Production Volumes

Project Partitioning

Project Cloning

Reticle Floorplaning

Shotmap Definition

Dicing Plan Definition

Reticle, Wafer Shotmap, Wafer Dicing Plans


Multi project reticle design wafer dicing under uncertain demand

Why is Dicing a Problem?

  • Side-to-side dicing!

  • Correctly sliced out dies

    • Cut lines along all four edges

    • No cut line partitioning the die

Standard wafer dicing

MPW dicing


Multi project reticle design wafer dicing under uncertain demand

Side-to-side Dicing Problem

Given:

  • Production volume for each die

  • Reticle floorplan

  • Wafer shot-map

    Find:

  • Horizontal and vertical dicing plans for each wafer

    To Minimize:

  • #wafers required to meet production volumes


Multi project reticle design wafer dicing under uncertain demand

Dicing Strategies

2

2

2

1

1

1

3

3

3

4

4

4

  • Wafer Dicing Plan (DP): all horizontal and vertical cut lines used to cut a wafer

  • Row/Column DP: cut lines through row/column of reticle images

  • Single wafer dicing plan (SDP) [ISPD04] [KahngR04]

    • The same wafer DP used for all wafers

    • Different DPs used for different rows/cols in a wafer

  • Multiple wafer dicing plans (MDP)

    • Restricted MDP: the same DP used for all rows/cols of a wafer

    • Graph coloring based heuristic in [Xu et al. 04]


Independent dies

Independent Dies

  • Under restricted MDP dicing, all reticle images on wafer yield the same set of dies

  • Independent set: set of dies that that can be simultaneously diced from a reticle image

    • Only maximal independent sets are of interest!

2

1

3

4

Maximal Independent Sets: {1, 4} {2} {3}


Ilp for restricted mdp

ILP for Restricted MDP


Multi project reticle design wafer dicing under uncertain demand

CMP Floorplan


Multi project reticle design wafer dicing under uncertain demand

SDP vs. MDP

5 wafers with MDP

9 wafers with SDP


4 part dicing

4-Part Dicing

  • Partition each wafer into 4 parts then dice each part separately using side-to-side cuts


Multi project reticle design wafer dicing under uncertain demand

Design Flow for MPW

Die sizes + Production Volumes

Project Partitioning

Project Cloning

Reticle Floorplaning

Shotmap Definition

Dicing Plan Definition

Reticle, Wafer Shotmap, Wafer Dicing Plans


Multi project reticle design wafer dicing under uncertain demand

Shotmap #1

Shotmap #2

Shotmap Definition Problem

?

Reticle Floorplan

  • Simple grid-based shotmap definition algorithm yields an average reduction of 13.6% in #wafers


Multi project reticle design wafer dicing under uncertain demand

Design Flow for MPW

Die sizes + Production Volumes

Project Partitioning

Project Cloning

Reticle Floorplaning

Shotmap Definition

Dicing Plan Definition

Reticle, Wafer Shotmap, Wafer Dicing Plans


Multi project reticle design wafer dicing under uncertain demand

Reticle Floorplaning Problem

  • Given:

    • Die sizes & production volumes

    • Maximum reticle size

  • Find:

    • Placement of dies within the reticle

  • To Minimize:

    • Production cost (reticle cost, #wafers, …)


Multi project reticle design wafer dicing under uncertain demand

Reticle Floorplaning Methods

  • Key challenge: cost estimation

  • Previous approaches

    • Simulated annealing [ISPD04]

    • Grid-packing [Andersson et al. 04, KahngR04]

    • Integer programming [WuL05]

  • Our approach: Hierarchical Quadrisection (HQ)


Multi project reticle design wafer dicing under uncertain demand

Hierarchical Quadrisection Floorplan

  • At most one die assigned to each region at lowest level

  • Region widths/heights easily computed from die assignment

  • HQ mesh more flexible than grid


Multi project reticle design wafer dicing under uncertain demand

HQ Algorithm

  • Random initial assignment improved using simulated annealing

    • SA moves: region exchange, die rotation

    • Max reticle size enforced throughout the algorithm

  • Hierarchical structure enables quick cost estimation


Multi project reticle design wafer dicing under uncertain demand

HQ Floorplan of CMP Testcase

Reticle Area =2.30(vs. 2.45)

4 wafers with MDP (vs. 5)


Multi project reticle design wafer dicing under uncertain demand

Design Flow for MPW

Die sizes + Production Volumes

Project Partitioning

Project Cloning

Reticle Floorplaning

Shotmap Definition

Dicing Plan Definition

Reticle, Wafer Shotmap, Wafer Dicing Plans


Multi project reticle design wafer dicing under uncertain demand

Project Cloning

  • Motivation

    • Die-to-die inspection [Xu et al.]

    • Reduced wafer cost when there is large variation in production demands

  • Post-processing approach [WuL05]

    • Insert clones in white space left on reticle

  • Our approach

    • Before floorplaning: number of clones proportional to square root of production volume; clones arranged in clone arrays

    • During floorplaning: clone arrays assigned to single cell in HQ; new SA moves: add/delete clone array row/column

    • After floorplaning: insert additional clone array rows/columns without increasing cell size


Multi project reticle design wafer dicing under uncertain demand

Design Flow for MPW

Die sizes + Production Volumes

Project Partitioning

Project Cloning

Reticle Floorplaning

Shotmap Definition

Dicing Plan Definition

Reticle, Wafer Shotmap, Wafer Dicing Plans


Multi project reticle design wafer dicing under uncertain demand

Schedule Aware Partition

  • More decision knobs: fabrication schedule

I will not pay you afterJune

?

But, money will be saved if waiting for other orders…

  • Project Partitioning Problem

    • Given: Reticle size, set of projects

    • Find:Partition of projects into reticles

    • To minimize: Sum of manufacturing cost and delay cost

  • [BACUS05] Schedule-aware partitioning leads to an average cost reduction of 63.8% vs. schedule-blind partitioning


Multi project reticle design wafer dicing under uncertain demand

Demand Uncertainty

  • Customer demands (over reticle life period) may not be fully known at design time

    • Only rough customer demand distribution available (e.g., min/max demand)

  • MPW become even more attractive in this context: sharing of demand misprediction risks

  • Online wafer dicing combined with production of larger wafer lots can bring further economies of scale (see paper)

    • Feasible when there are no IP protection issues


Multi project reticle design wafer dicing under uncertain demand

Robust Reticle Floorplaning

  • Given:

    • Die sizes

    • Maximum reticle size

    • Distribution of customer orders

  • Find:

    • Placement of dies within the reticle

  • To Minimize:

    • Expected #wafers required to meet customer orders over a fixed time horizon


Multi project reticle design wafer dicing under uncertain demand

Compared Algorithms

  • HQ with production volume set to the expected customer demand

  • HQ+Cloning with production volume set to the expected customer demand

  • Distribution-driven simulated annealing

    • Use expected production cost for evaluating SA moves

    • Monte-Carlo simulation used to estimate expected cost


Multi project reticle design wafer dicing under uncertain demand

Robustness Results - Normal


Multi project reticle design wafer dicing under uncertain demand

Robustness Results – Uniform


Conclusions future research

Conclusions & Future Research

  • Improved MPW design flow

    • Schedule-aware partitioning: 60% average cost reduction

    • Project cloning: 10% average wafer cost reduction

    • HQ reticle floorplan: 15% average wafer cost reduction

    • Wafer shot-map definition: 13% average wafer cost reduction

    • MDP wafer dicing: 60% average wafer cost reduction

  • Future work

    • Multi-layer reticle design


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