Semiconductor IndustryDetailed Scheduling Solutions

OPTIMAL INTELLIGENT SCHEDULING

INCREASE

REDUCE

IMPROVE

WIP Inventory

Waiting Times

Changeovers

Inventory

Total Cycle Time

Synchronization

REDUCE

SHRINK

REDUCE

SLASH Costs

Semiconductor manufacturing is driven by the demands of consumer electronics. In response to shorter product lifecycles seen in consumer electronics, semiconductor fabrication plants (called fabs) are required to produce smaller lots of chips so that they can efficiently switch production to respond to requirements of a variety of electronic devices as they rapidly emerge in the marketplace. Another important goal is to reduce fabrication time by reducing the waiting time between processing steps thus improving throughput and OEE (Overall Equipment Effectiveness) and reducing cost per lot.

At the same time, there is pressure to keep up with technological advancement; for instance the current state-of-the-art for wafer size is considered to be 300 mm (12 in), however, the industry is aiming to move to the 450 mm wafer size. Line widths have been reduced from 65 to 22 nm with a further objective of 16 nm. Additionally, there is a large push to completely automate the production of semiconductor chips from beginning to end.

Thus the key challenges for the semiconductor industry are the pressure of advancing technology, shorter product life cycles and the need to meet delivery commitments while staying cost competitive. Synchronization of scheduling within and across the dif-ferent areas of a fab and changeover/setup time optimization is key to reducing waiting times and improving throughput.

Benefits of Optimal Scheduling

Scheduling within and across areas of a fab is complex problem. This is the point at which Optessa technology can make a significant contribution towards meeting the scheduling challenges of the semiconductor industry.

Optessa specializes in creating elegant solutions for “impossible” optimization problems with no easy solution – typically large / complex, real world planning and scheduling problems. Optessa has a proven track record of providing optimal and effective solu-tions to complex planning, scheduling and sequencing problems.

Optessa’s focus is on optimization of scheduling problems involving high volume and variety with a large numbers of constraints and rules – as is the case with the semiconductor indus-try. Optessa solutions use modern stochastic techniques to optimize planning, scheduling and sequenc-ing for different manufacturing in-dustries. Customers achieve signif-icant cost and profitability benefits immediately upon implementing Optessa solutions. The chart shows the estimated monthly savings optimal scheduling can achieve in a large 300 mm fab:

Semiconductor Manufacturing

Two products from the Optessa solutions suite are especially relevant in meeting the challenges of scheduling in the semiconductor industry.

Optessa MLS: Optessa MLS is specifically designed to address the complex sequencing and scheduling requirements of manufacturing industries with product variety, large volumes and multiple lines/ plants. Optessa MLS generates high quality, near optimal line sequences and schedules. MLS has an established track record of enabling manufacturers to reduce order to de-livery lead times, reduce inventories, and smooth production to fulfil each order while reducing manufacturing costs.

The quality and evenness of an Optessa MLS schedule is vastly superior to a schedule generated by other techniques. The Optessa MLS algorithms can generate a near optimal solution after considering all the rules and constraints. Based on modern optimization techniques and em-bodying patented algorithms, the powerful computational engine optimizes the entire sched-ule. As a result, the system rapidly produces near optimal schedules. Optessa MLS can be applied to scheduling the flow across different areas of a fab.

Optessa RTS: Optessa RTS is a unique solution for the real-time event driven scheduling needs of modern automated manufacturing plants in diverse industries such as automotive, semicon-ductor, electronics, food & beverage etc. and also in warehousing / logistics operations to enable optimized real-time order fulfillment. Optessa RTS combines powerful optimization, based on the Optessa sequencing and scheduling engine, with a real-time architecture. The system is typically integrated with plant level MES / RTD systems and combines predictive optimization with tracking of upstream stages. Optessa RTS is capable of generating optimal scheduling/se-quencing and routing decisions for a single processing step such as Photolithography or Diffu-sion. Optessa RTS solutions have been demonstrated to be significantly superior to custom logic developed in MES systems or programmed into RTD systems. The following table illustrates the applicability of Optessa solutions in the semiconductor indus-try:

Time horizon Minutes to hours Days to weeks

Fab scheduling MLS MLS

Area scheduling(e.g. Frontend, Backend) MLS MLS

Step scheduling(e.g. Photolithography) RTS

Tool scheduling RTS

Optessa Products

Scheduling All Operations of Semiconductor Manufacturing

Optessa can schedule and synchronize across all areas and steps of a semiconductor fab. Fabs typically consist of frontend and backend areas as illustrated by the image below: .

Fab Scheduling Requirements and Optessa FeaturesThe semiconductor industry has specific requirements for scheduling, and Optessa’s solutions have unique strengths to meet these requirements as illustrated in the tables below:

Frontend - Photo-Litho

Photo-Litho Scheduling Requirement Optessa Feature

Throughput: Photo-Litho is considered to be the bottleneck on the frontend. A schedule should appropriately trade-off WIP against cycle-time to optimize throughput out of the photo-litho area.

Optessa looks at upstream and downstream WIP to balance the load across areas when generating a predictive and global optimized schedule

Re-entrant Flows: Wafers can revisit the same tool at different stages of their process flow, so that wafers at different stages of their man-ufacturing cycle compete with each other for resources.

Optessa enforces precedence, time window and priority relationships across job classes, and devel-ops optimal schedules considering all aspects of re-entrant flows.

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Photo-Litho Scheduling Requirement Optessa Feature

Critical Layers: Tool that processed first critical layer must also process subsequent critical lay-ers.

Optessa has unique notion of “schedule bias” in which processing of subsequent critical layers can be constrained to the tool that processed the first layer.

Non-critical Layers: Criteria for “Where Next?” should consider all routing options, and op-timize taking into account queue times, tool balancing & lot priorities.

Optessa can make complex routing choices using a flexible cost function that can incorporate waiting times, load balance and task priorities

Reticle Management: Minimize reticle change-overs / maximize reticle trains, while enforcing reticle constraints related to max uses between inspections

Optessa has built-in constraint types that minimize changeovers, maximize “run lengths”, and enforce max usage limits

Hot Lots: Expedite hot lots while considering queue times, lot priority, tool balancing and reticle availability

Optessa has a variety of features to support lot pri-orities and preferential scheduling, including rules for due dates, smoothing and resource availability

Frontend - Diffusion

Diffusion Scheduling Requirement Optessa Feature

Batching: Need to batch different lots based on recipes so as to optimally trade-off delays vs. throughputs

Optessa has extensive batching functionality that can optimize batch composition while optimizing other schedule metrics.

Process Timings: Lots have to be batched & processed within limited time window or be scrapped

Optessa enforces process time windows and rule priorities so that process timings are satisfied

Backend: ATM

Diffusion Scheduling Requirement Optessa Feature

Downstream Smoothing: Smooth production flows and achieve load balance despite high pro-cess time & batch size variability

Optessa supports process times that vary by tool, by recipe, batch size etc, and can smooth by any attribute, including downstream destination

Smooth violations: Any rule violations should be smoothed over schedule horizon, and should not be lumped

Optessa not only minimizes violations, but default behavior is to ensure even schedule quality over entire horizon

ATM Scheduling Requirement Optessa Feature

Flow type manufacturing: Sequential operations per product with unidirectional flow

Optessa has been widely deployed and validated in flow shops. Supports serial / parallel machine config-urations and has been used to schedule bottlenecks + every machine / line in a plant.

Process Times: Vary by product and by machine type

Optessa supports process times that can vary by product, by machine and even over time

Product Variety, and Demand Volatility: High, because ATM can support multiple fabs, and demands can change close to production date

Optessa MLS excels when the number of variants is large. In principle, each lot can belong to a distinct product family.

Schedule Objectives: Maximize due date adher-ence, minimize tardiness, maximize utilization, minimize WIP etc

Business objectives can be expressed in terms of built-in MLS constraints, and optimizer will minimize overall cost function

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ATM Scheduling Requirement Optessa Feature

Batching: Group fixed number of wafers into a lot that is scheduled & processed

Optessa has extensive batching functionality that can optimize batch composition while optimizing other schedule metrics.

Sequence Dependent Setups: setup times whenever a machine switches btw operations or product families

Optessa has extensive capabilities to represent com-plex sequence dependent setup rules and optimize schedules in such environments.

Complex routing: 10s of product families, 100s of machines, operations & routes vary by prod-uct family

Optessa supports sequence dependent setup times that can vary by product pairs, by machine and even over time

Dedicated Machines: Certain machines can only handle specific operations / products

Optessa supports hard and soft “line restrictions” that enforce product to machine mapping rules

Preventive Maintenance, Engineering Times: Non-production activities should be considered / scheduled

Optessa models a variety of “null jobs” unrelated to production which can be manually scheduled, or optimally scheduled

Schedule Stability: Schedule changes should be minimized during re-scheduling

Unique capability of rescheduling with bias” that maintains schedule stability even under changing conditions (orders, capacity, con-straints)

Optimal Intelligent Scheduling

Key Optessa Strengths

OPTIMAL INTELLIGENT SCHEDULING

About Optessa

Optessa Inc. is the emerging leader in Planning, Sequencing and Scheduling Technology with considerable experience in applying cutting edge optimization advances to solve real world prob-lems. Optessa’s customers include some of the largest global brand manufacturing companies in the world. To learn more about how Optessa can help you today, please visit: www.optessa.com, e-mail: info@optessa.com

• Near optimal solutions generated by powerful proprietary algorithms

• Evenly favorable solution across entire schedule

• Powerful representation model for all types of area & tool configura-tions

• Comprehensive set of rules and constraints handled

• Native re-scheduling capabilities

• Configurable system: data dictionary, parameter tables

• “Light touch”: can be integrated & embedded with existing MES / Controller / Dispatch systems

• Enhance “What Next” and “Where Next” functionalities with true re-al-time optimization