Welcome back to the Flexciton Tech Glossary Series: A Deep Dive into Semiconductor Technology and Innovation. Our second entry of the series is all about Batching. Let's get started!

A source of variability

Let's begin with the basics: what exactly is a batch? In wafer fabrication, a wafer batch is a group of wafers that are processed (or transported) together. Efficiently forming batches is a common challenge in fabs. While both logistics and processing both wrestle with this issue, our article will focus on batching for processing, which can be either simultaneous or sequential.

Simultaneous batching is when wafers are processed at the same time on the same machine. It is very much inherent to the entire industry, as most of the machines are designed for handling lots of 25 wafers. There are also process types – such as thermal processing (e.g. diffusion, oxidation & annealing), certain deposition processes, and wet processes (e.g. cleaning) – that benefit from running multiple lots in parallel. All of these processes get higher uniformity and machine efficiency from simultaneous batching.

On the other hand, sequential batching refers to the practice of grouping lots or wafers for processing in a specific order to minimise setup changes on a machine. This method aims to maximise Overall Equipment Effectiveness (OEE) by reducing the frequency of setup adjustments needed when transitioning between different production runs. Examples in wafer fabrication include implant, photolithography (photo), and etch. 

Essentially, the entire process flow in wafer manufacturing has to deal with batching processes. To give a rough idea: a typical complementary metal-oxide semiconductor (CMOS) architecture in the front-end of the line involves batching in up to 70% of its value added steps. In a recent poll launched by FabTime on what the top cycle time contributors are, the community placed batching at number 5^[1], behind tool downs, tool utilisation, holds, and one-of-a-kind tools. Batching creates lot departures in bursts, and hence it inherently causes variability in arrivals downstream. Factory Physics states that:

“In a line where releases are independent of completions, variability early in a routing increases cycle time more than equivalent variability later in the routing.” ^[2]

Successfully controlling this source of variability will inevitably result in smoother running down the line. However, trying to reduce variability in arrival rates downstream can lead to smaller batch sizes or shorter campaign lengths, affecting the effectiveness of the batching machines themselves.

The many complexities of batching

In wafer fabs, and even more so in those with high product mix, batching is particularly complicated. As described in Factory Physics:

"In simultaneous batching, the basic trade-off is between effective capacity utilisation, for which we want large batches, and minimal wait to batch time, for which we want small batches.” ^[2]

For sequential batching, changing over to a different setup of the machine will cause the new arriving lots to wait until the required setup is available again.

In both cases, we’re talking about a decision to wait or not to wait. The problem can easily be expressed mathematically if we’re dealing with single product manufacturing and a low number of machines to schedule. However, as one can imagine, the higher the product mix, the higher the possible setups and machines. Then the problem complexity increases, and the size of the solution space explodes. That’s not all, there are other factors that might come into play and complicate things even more. Four different examples are:

• Timelinks or queue time constraints: a maximum time in between processing steps
• High-priority lots: those that need to move faster through the line for any reason
• Downstream capacity constraints: machines that should not get starved at any cost
• Pattern matching: when the sequence of batching processes need to match a predefined pattern, such as AABBB

Strategies to deal with batching

Historically, the industry has used policies for batching; common rules of thumb that could essentially be split up into ‘greedy’ or ‘full batch’ policies^[3]. Full batch policies require lots to wait until a full batch is available. They tend to favour effective capacity utilisation and cost factors, while they negatively impact cycle time and variability. Greedy policies don’t wait for full batches and favour cycle time. They assume that when utilisation levels are high, there will be enough WIP to make full batches anyway. For sequential batching on machines with setups, common rules include minimum and maximum campaign length, which have their own counterpart configurations for greedy vs full batching.^[3] 

The batching formation required in sequential or simultaneous batching involves far more complex decisions than that of loading a single lot into a tool, as it necessitates determining which lots can be grouped together. Compatibility between lots must be considered, and practitioners must also optimize the timing for existing lots on the rack to await new arrivals, all with the goal of maximising batch size. ^[4]

Industrial engineers face the challenge of deciding the best strategy to use for loading batch tools, such as those in the diffusion area. In an article by FabTime ^[4], ^[5] the impact of the greedy vs full or near full batch policy is compared. The greedy heuristic reduces queuing time and variability but may not be cost-effective. Full batching is cost-effective but can be problematic when operational parameters change. For instance, if a tool's load decreases (becomes less of a bottleneck), a full batch policy may increase cycle time and overall fab variability. On the other hand, a greedy approach might cause delays for individual lots arriving just after a batch is loaded, especially critical or hot lots with narrow timelink windows. Adapting these rules to changing fab conditions is essential.

In reality, these two policies are extreme settings in a spectrum of possible trade-offs between cost and cycle time (and sometimes quality). To address the limitations of both the greedy and full batch policies, a middle-ground approach exists. It involves establishing minimum batch size rules and waiting for a set duration, X minutes, until a minimum of Y lots are ready for batching. This solution usually lacks robustness because the X and Y values depend on various operational parameters, different recipes, product mix, and WIP level. As this rule-based approach incorporates more parameters, it demands greater manual adjustments when fab/tool settings change, inevitably leading to suboptimal tool performance.

In all of the above solutions, timelink constraints are not taken into consideration. To address this, Sebastian Knopp^[6] recently developed an advanced heuristic based on disjunctive graph representation. The model's primary aim was to diminish the problem size while incorporating timelink constraints. The approach successfully tackled real-life industrial cases but of an unknown problem size.

Over the years, the wafer manufacturing industry has come up with various methodologies to help deal with the situation above, but they give no guarantee that the eventual policy is anywhere near optimal and their rules tend to stay as-is without adjusting to new situations. At times, this rigidity has been addressed using simulation software, enabling factories to experiment with various batching policy configurations. However, this approach proved to be resource-intensive and repetitive, with no guarantee of achieving optimal results.

How optimization can help master the batching problem

Optimization is the key to avoiding the inherent rigidity and unresponsiveness of heuristic approaches, helping to effectively address the batching problem. An optimization-based solution takes into account all batching constraints, including timelinks, and determines the ideal balance between batching cost and cycle time, simultaneously optimizing both objectives.

It can decide how long to wait for the next lots, considering the accumulating queuing time of the current lots and the predicted time for new lots to arrive. No predetermined rules are in place; instead, the mathematical formulation encompasses all possible solutions. With a user-defined objective function featuring customised weights, an optimization solver autonomously identifies the optimal trade-off, eliminating the need for manual intervention.

The challenge with traditional optimization-based solutions is the computational time when the size and complexity of the problem increase. In an article by Mason et al.^[7], an optimization-based solution is compared to heuristics. While optimization outperforms heuristics in smaller-scale problems, its performance diminishes as problem size increases. Notably, these examples did not account for timelink constraints.

This tells us that the best practice is to try to break down the overall problem into smaller problems and use optimization to maximise the benefit. At Flexciton, advanced decomposition techniques are used to break down the problem to find a good trade-off between reduced optimality from the original problem and dealing with NP-hard complexity.^[8]

Many practitioners aspire to attain optimal solutions for large-scale problems through traditional optimization techniques. However, our focus lies in achieving comprehensive solutions that blend heuristics, mathematical optimization, like mixed-integer linear programming (MILP), and data analytics. This innovative hybrid approach can vastly outperform existing scheduling methods reliant on basic heuristics and rule-based approaches.

Going deeper into the solution space

In a batching context, the solution space represents the numerous ways to create batches with given WIP. Even in a small wafer fab with a basic batching toolset, this space is immense, making it impossible for a human to find the best solution in a multi-product environment. Batching policies throughout history have been like different paths for exploring this space, helping us navigate complex batching mathematics. Just as the Hubble space telescope aided space exploration in the 20th century, cloud computing and artificial intelligence now provide unprecedented capabilities for exploring the mathematical world of solution space, revealing possibilities beyond imagination.

With the advent of these cutting-edge technologies, it is now a matter of finding a solution that satisfies the diverse needs of a fab, including cost, lead time, delivery, quality, flexibility, safety, and sustainability. These objectives often conflict, and ultimately, finding the optimal trade-off is a business decision, but the rise of cloud and AI will enable engineers to pinpoint a batching policy that is closest to the desired optimal trade-off point. Mathematical optimization is an example of a technique that historically had hit its computational limitations and, therefore, its practical usefulness in wafer manufacturing. However, mathematicians knew there was a whole world to explore, just like astronomers always knew there were exciting things beyond our galaxy. Now, with mathematicians having their own big telescope, the wafer manufacturers are ready to set their new frontiers.

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Authors
Ben Van Damme, Industrial Engineer and Business Consultant, Flexciton
Dennis Xenos, CTO and Cofounder, Flexciton

References

[1] FabTime Newsletter: Issue 24.03

[2] Wallace J. Hopp, Mark L. Spearman, Factory Physics: Third Edition. Waveland Press, 2011

[3] Lars Mönch,  John W. Fowler,  Scott J. Mason, 2013, Production Planning and Control for Semiconductor Wafer Fabrication Facilities, Modeling, Analysis, and Systems, Volume 52, Operations Research/Computer Science Interfaces Series 

[4] FabTime Newsletter: FabTime Cycle Time Tip of the Month #4: Use a Greedy Policy when Loading Batch Tools

[5] FabTime Newsletter: Issue 9.03 

[6] Sebastian Knopp, 2016, Complex Job-Shop Scheduling with Batching in Semiconductor Manufacturing, PhD thesis, l’École des Mines de Saint-Étienne 

[7] S. J. Mason , J. W. Fowler , W. M. Carlyle & D. C. Montgomery, 2007, Heuristics for minimizing total weighted tardiness in complex job shops, International Journal of Production Research, Vol. 43, No. 10, 15 May 2005, 1943–1963   

[8] S. Elaoud, R. Williamson, B. E. Sanli and D. Xenos, Multi-Objective Parallel Batch Scheduling In Wafer Fabs With Job Timelink Constraints, 2021 Winter Simulation Conference (WSC), 2021, pp. 1-11

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To cloud, or not cloud, that is the question.

Some might consider the opening statement a tad flippant in borrowing Hamlet's famous soliloquy. Yet, the internal struggle our hero feels agonising over life and death holds a certain likeness to the challenges faced by Fab Managers today. Businesses live and die by their decisions to either embrace or disregard new innovations to gain a competitive edge and nowhere is this truer than in the rough and tumble world of semiconductor manufacturing; Fairchild, National Semiconductor and S3 are just a few of those who did not last. ^[1][2][3]‍

Semiconductor manufacturing has had a long history of innovating, tweaking, and tinkering,^[4] so it’s somewhat surprising that the sentiment towards cloud uptake has been weaker in the semiconductor industry compared to the wider market^[5]. This article aims to explore some of the potential benefits of cloud adoption to better equip Fab Managers with the motivation to take another look at the cloud question.

Recap: What are the different types of Cloud?

Cloud computing encompasses public, private, and hybrid models. The public cloud (think Azure, AWS, Google Cloud and so on) offers rental of computational services over the internet, while the private cloud replicates cloud functionality on-premises. However, private clouds require a significant upfront investment, ongoing maintenance costs and a skilled in-house IT team to manage and maintain the infrastructure, making it a less appealing option for smaller firms. Hybrid cloud blends on-site and cloud resources for flexible workloads, segregating the most sensitive workloads to on-premise environments for the greatest control; however, control does not necessarily mean security, which will be discussed in a later article! 

Understanding the benefits of cloud

1.      The Latest Tech

Embracing the latest cloud technology offers wafer fab facilities, not just organisations, a direct path to heightened capabilities in their manufacturing processes through the use of digital and smart manufacturing technologies. By harnessing advanced computational powers such as real-time analytics; optimization^[6]; and machine learning defects detection^[7], fabs can maximise all their fundamental KPIs, ultimately leading to better business outcomes. McKinsey estimates that, compared to other semiconductor activities, manufacturing has the most to gain from the AI revolution (Fig. 1), and a key technology enabling this is will be the vast computational power of the cloud.^[8]

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Case Study: The Latest Tech Driving Improvements in Fab KPIs

Seagate achieved a 9% increase in moves by utilising Flexciton’s cloud native platform and cutting-edge autonomous scheduling.

2. Redundancy, Scaling, Recovery and Updates

It is true that some of these technologies can be provided on-premises; however, cloud computing, in general, reduces downtime through redundancy, automated scaling, and disaster recovery mechanisms, ensuring seamless operation even during hardware failures or unexpected traffic spikes. Some estimates suggest that downtime can cost firms an eye-watering $1 million to $5 million per hour, depending on their size and sector. ^[9] By leveraging the cloud, the cost of operating disaster recovery services has demonstrated potential cost savings of up to 85% when comparing public to private options. ^[10] It is easy to speculate that for wafer fab critical infrastructure, the cost of downtime could be significantly higher.

Furthermore, the number of wafers processed within a fab can cause computational traffic spikes during busy periods for some applications. On-premises deployments would need to account for this, even if the resource is not in use all the time, which can add to inefficiencies, while public cloud can elastically scale down, meaning you only pay for what you use. 

Lastly, on-premises systems without the ability to monitor and update remotely are often many versions behind, prioritising perceived stability but research has shown increasing the rate of software iteration increases stability and resilience rather than weakening it. ^[11] Without the convenience of remote updates, legacy systems can become entrenched, with employees on the shop floor being hesitant to embrace change due to the fear of disrupting critical infrastructure and the expenses associated with upgrading IT infrastructure. This sets in motion a self-reinforcing cycle where the expenses and associated risks of transitioning increase over time, ultimately resulting in significant productivity losses as users continue to rely on outdated technology from decades past.

3. Specialisation and Comparative Advantage

Stepping back from the fab and taking a holistic view of the semiconductor manufacturing organisation reveals compelling economic arguments, both on macro and micro scales, for embracing cloud.

Allowing cloud providers to specialise in cloud computing while wafer fab manufacturers focus solely on wafer fabrication benefits the latter by freeing them from the complexities of managing IT infrastructure. ^[12] This collaboration allows wafer fab manufacturers to allocate their resources towards core competencies, leading to increased operational efficiency and superior wafer production.

Simply put, fabs do not build the complex tools they need to make their products, such as photolithography equipment; they purchase and utilise them in ways others can’t to produce market leading products. Why should utilising the tools of the cloud be any different?

On a macro level, the argument of specialisation also applies through comparative advantage.^[13] Different continents and countries have comparative advantages in certain fields, Asia has long been a world leader in all kinds of manufacturing due to its vast populations.^[14] The United States, on the other hand, has a tertiary education system which is the envy of the world; institutions like Stanford and MIT are household names across the globe, and this has provided the high technical skills needed to be the home of the technology start up. Utilisation of cloud technology and other distributed systems allows firms to take the best of what both regions have to offer, high tech manufacturing facilities from Singapore to Taiwan with the latest technology from Silicon Valley or perhaps London. Through the cloud, Fab Managers and organisations can leverage a single advanced technology across multiple fabs within complex supply chains. This eliminates the need for costly and experienced teams to travel across the globe or manage multiple teams in various locations with varying skill sets, all while locating facilities and offices where the best talent is.

In brief, semiconductor firms' fate could rest on one pivotal decision: adoption of cloud. This choice carries the promise of leveraging cutting-edge technology, fortifying resilience, and reaping a multitude of advantages. Notably, by transitioning to cloud-native solutions, Fab Managers can usher their organisations into an era of unparalleled competitiveness, all while enjoying a range of substantial benefits. Among these benefits, for example, is cloud-native architecture like Flexciton’s, promising lower cost of ownership and zero-touch maintenance for fabs. We will delve deeper into the crucial aspect of security in one of our upcoming blogs, providing a comprehensive understanding of how cloud-native solutions are actually key to safeguarding sensitive data and intellectual property, rather than compromising it. In this era of constant innovation, embracing the cloud is more than just an option; it’s becoming a strategic imperative.

Author: Laurence Bigos, Product Manager at Flexciton

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References

[1] Investor relations - Texas Instruments completes acquisition of National Semiconductor - Texas Instruments

[2] ON Semiconductor Successfully Completes Acquisition of Fairchild Semiconductor for $2.4 Billion in Cash

[3] S3 Graphics: Gone But Not Forgotten | TechSpot

[4] Miller, C. (2022). Chip War: The Fight for the World's Most Critical Technology. Scribner.

[5] Flexciton | Blog & News | Is Fear Holding Back The Chip Industry’s Future In The Cloud?

[6] Flexciton | Resources | Seagate Case Study 2.0

[7] Lynceus: Inline, Real-time, AI Based Process Control Monitoring That Can Reduce Inspection & Metrology Capex (semianalysis.com)

[8] Applying artificial intelligence at scale in semiconductor manufacturing | McKinsey

[9] Know Key Disaster Recovery Statistics And Save Your Business (invenioit.com)

[10] Wood.pdf (usenix.org)

[11] Forsgren, N., Humble, J., & Kim, G. (2018). Accelerate: The Science of Lean Software and DevOps. IT Revolution Press.

[12] Specialization Definition (investopedia.com)

[13] What Is Comparative Advantage? (investopedia.com)

[14] Why China Is "The World's Factory" (investopedia.com)

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At Flexciton, we often talk about how autonomous scheduling allows wafer fabs to surpass the need for maintaining many rules to enable the behaviours they want at different toolsets. I would like to offer an analogy to show how significant the difference is.

Navigating the City

Imagine you are a passenger in a taxi. Your driver is a local; they know every road like the back of their hand and know the best routes to avoid likely problems. They can be flexible and effective, but have to spend a long time thinking about how to get to your destination. They also can’t know about the traffic on each potential route, and for new destinations they may require some trial and error before they find a good way of getting there. Worst of all, though they might have accumulated some great stories from their years of driving, it’s only thanks to those many years that they can navigate with any level of mastery.

Now imagine you have a very basic robotic driver; this driver is so mechanical that it has a hard-coded rule for every single road and junction: “If I’m at junction 20, I wait exactly thirty seconds and then I turn left.” This rule has come from an engineer performing a time study based on traffic levels six months ago. The driver has no knowledge of local events happening (for example, if it turns out that there is no oncoming traffic right now), and doesn’t even change its decisions when you need it to navigate to a new destination!

Meanwhile, when local conditions change at all (gaps in oncoming traffic at junction 20 are now every twenty seconds on average!) an engineer needs to manually change that parameter in the robot’s logic. And if the overall conditions change everywhere, or a new destination is desired, every rule needs to be retuned.

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Finally, imagine a truly autonomous taxi. This taxi has a navigation system that knows where the traffic is, assesses the speed of every potential route, reacts to changes in conditions, and can get you to exactly where you want to go. In fact, all you have to do is tell it the destination; then you can sit back and relax, knowing it will get you there in the shortest possible time.

Navigating the Fab

While many wafer fabs have moved away from relying purely on tribal knowledge of manufacturing specialists on the fab floor, the scheduling problem in semiconductor factories is so difficult that, until recently, the hard-coded robotic taxi driver was the state-of-the-art. These solutions ask industrial engineers to manually tune thousands of rules to achieve intelligent behaviour, and they must be continuously re-tuned as fab conditions change.

A common scheduling challenge is deciding when to allow wafers into a timelink (or queue time loop) at diffusion. A timelink is the maximum amount of time that can elapse between two or more consecutive process steps, and some schedulers will simply limit the number of lots allowed within the timelinked steps at any one time. Others will just use a priority weight given to all timelinked lots, so that they are more likely to move through the loop without violating their time limit. Both of these rules are manually tuned and can’t react to the conditions of that particular moment in time, leading either to rework or scrap, or unnecessarily high cycle times.

Another typical example from a commonly-used heuristic scheduler is the application of minimum batch size rules at diffusion areas. A typical rule might be “wait for a minimum batch size of x, unless y minutes have elapsed, in which case dispatch whatever is at the rack.” Many fabs will set up this rule for every furnace-operation combination, which could mean ~3,000 manually tuned parameters just for one rule at one toolset.

Meanwhile, when micro conditions change, for example daily wip level fluctuations, these tuned parameters cannot react. And worse, when macro conditions such as overall market demand change, it makes it very hard for the whole fab to pivot quickly, because every rule needs re-tuning manually. Despite the theory that these rules can be set once every few months, in practice most fabs end up re-tuning these rules continuously, even daily, in order to maintain reasonable performance - accepting the predictable impact on industrial engineering resources that has!

Optimized scheduling, however, does away with these rules entirely and directly calculates the optimal schedule to improve your chosen objectives. In the timelink example, it doesn’t need to rely on guessing how many lots can be allowed into the loop - it just calculates the optimal schedule for the multiple steps involved, ensuring no timelink violations will occur.

But still, how do you get the scheduler to do what you want?

A New Paradigm for Tuning

If you have read any of our previous articles, you may be aware that optimization-based scheduling uses objectives such as “minimise queue time” and “maximise batch size” to calculate the optimal schedule. In fact, on most of our toolsets we only use ~2-3 objective weights, and by setting these you can achieve the balance and results you want.

Even this, however, is not truly autonomous.

We’ve been working to bring forward a new paradigm: letting you choose the fab-level outcome you want directly - like setting the destination for the taxi. If you know you want to prioritise achieving higher throughput, you can just specify that and Flexciton’s autonomous scheduler will automatically figure out what the optimization objective needs to be to achieve it.

What does this mean? It means you directly control the fab outcome you want to achieve, rather than guessing what toolset-level behaviours will produce the fab-level KPIs you want.

Orders of Magnitude

So when we speak about autonomous scheduling, we are referring to this new paradigm where you can choose the outcome you want, and Flexciton automatically does the rest. Instead of ~3,000 manually tuned parameters for just one of many rules at one toolset, just pick your desired KPI trade-off, and we automatically set the handful of objective weights that drive the optimization engine.

The result is not needing industrial engineering resource dedicated to tuning – instead, this valuable resource can be redeployed to work on higher value tasks. Moreover, it can enable consistent high performance across changes in fab conditions; and it becomes easier to pivot the entire fab’s direction when market conditions change.

This is how Flexciton’s scheduler is powerful enough to let you set the destination, and go.

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Author: Sebastian Steele, Product Manager at Flexciton

We are excited to introduce the Flexciton Tech Glossary Blog Series: A Deep Dive into Semiconductor Technology and Innovation.

In an ever-evolving semiconductor industry, understanding the nuances of new technologies and the transformative potential of artificial intelligence and optimization is paramount. The Flexciton Tech Glossary Blog Series is designed to shed light on specific technologies and innovations, offering insights into how these advancements can revolutionise semiconductor manufacturing operations.

Each article in this series will delve into a distinct theme, aiming to equip any practitioner in the industry from industrial engineers and manufacturing experts up to VP level professionals with the knowledge to integrate these innovations into their daily operations.

Beyond our in-house expertise, we’re excited to collaborate with industry experts, inviting them to contribute and enrich our series with their specialised knowledge and experience. Join us on this enlightening journey as we explore the frontiers of the semiconductor industry from A-Z.

AI will transform the semiconductor industry

Artificial Intelligence (AI) has become a transformative force in various sectors, driving a global wave of innovation and automation. Seemingly overnight, systems like ChatGPT that harness the primary human interface – natural language – have revolutionised how we interact with technology. In a similar vein, generative art technologies have reinvented our relationship with creativity, making it more accessible than ever before. These remarkable systems have acquired their capabilities through learning, fueled by training on vast amounts of data. This ongoing revolution prompts the question: what is the next frontier to be conquered?

Beyond the novel consumer applications leading the charge, the implications of AI in specialised fields, such as semiconductor manufacturing, are equally profound. Estimates place the earnings already achieved by AI across the semiconductor value chain at over $5 billion. The range of applications is immense and spans activities at all levels. From informing capital allocation, to demand forecasting, fab layout planning, and right down to chip design, AI can enable automation and increase efficiency. Semiconductor manufacturing, in particular, has been identified as the function presenting the most attractive opportunities, where the potential savings have been calculated to be over $10 billion in just the next few years [1].

Impact at all levels 

The semiconductor industry is facing several challenges where AI can make a significant impact. These span all the industry’s key activities: long-term capacity planning, research & design, sales, procurement and, of course, manufacturing. Some use cases that are increasingly gaining traction are:

• Supply Chain Optimization: Predictive analytics can forecast demand, optimize inventory levels, and enhance the overall efficiency of the supply chain [2]. 
• Automated Material Handling Systems (AMHS): Utilising AI-driven cognitive robotics within AMHS automates material transportation throughout the plant [3], optimizing production planning considering AMHS [4].
• Predictive Maintenance: AI can predict when equipment is likely to fail or require maintenance, reducing downtime and increasing overall equipment efficiency [5].
• Defect Detection: Advanced image recognition algorithms can identify defects in wafers at an early stage, ensuring higher yields and reducing wastage [6].
• Virtual metrology: AI can be deployed to estimate a product’s quality directly from production process data. This enables real-time quality monitoring without additional measuring steps [7]. 
• Process control: AI can analyse vast amounts of data to optimize the manufacturing process, ensuring the best conditions for each step and improving the overall quality of the chips (e.g. tool matching) [8].
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In this article, we focus on AI’s potential to automate scheduling within a semiconductor wafer fab and improve key metrics: increase the throughput of manufacturing lines, reduce cycle times and improve on-time delivery. But first, we step back and define both intelligence and artificial intelligence. 

Defining intelligence

Defining intelligence has been a long-standing challenge, with various perspectives offered. A widely-accepted definition, which broadly aligns with the context of semiconductor applications, is as follows:

‍Intelligence is the ability to accomplish complex goals. 

As suggested by Max Tegmark [9], intelligence is not universal but depends on the defined goal. As such, there are many possible types of intelligence. Extending this concept further, intelligence can be characterised according to the following features.

Goal type: Intelligence can be technical (problem-solving), social (interaction), or creative (idea generation).

Skill level: This is typically categorised as below/equivalent/super-human level. This determines whether we aim to match the performance of a human or surpass it.

Scope: Narrow intelligence specialises in a specific task, while broad intelligence encompasses a wide range of tasks like human intelligence.

Autonomy: Intelligence can operate with varying degrees of independence, from human-guided to fully autonomous.

In semiconductor scheduling, super-human performance level is necessary to sift through billions or even trillions of candidate solutions to derive optimal decisions, whilst adhering to complex constraints. Focusing on the narrow scope of scheduling allows the system to specialise, thereby optimizing its performance for these specific requirements. The technical nature of the task calls for a solution that exploits the strictly technical aspects to achieve superhuman performance. Finally, a system with high autonomy and no need for human intervention is desired in such a dynamic environment. 

Three important facets of Artificial Intelligence

AI involves creating models and machines that mimic human intelligence, including learning, reasoning, and decision-making. 

Learning is an important aspect of AI, relying on a model’s ability to iteratively refine its internal parameters until it can accurately capture underlying patterns. Machine Learning is the cornerstone approach for learning from data and techniques in this category can range from simple models like Linear Regression to complex Deep Learning networks. 

Reasoning involves drawing inferences based on established rules and facts, mimicking the human ability to logically connect information. It can aid in tasks like medical diagnosis (See the generative LLM AI from Google Med-Palm 2) or legal case analysis.  

Decision-making encompasses action exploration and problem-solving. Action exploration deals with determining actions through interaction with an environment, which can vary from well-defined scenarios, like a chess game, to unstructured situations, like driving a car. Problem-solving, on the other hand, focuses on finding solutions to clearly defined problems with specific objectives and constraints. This can involve simple tasks like sorting or more intricate challenges such as route planning, resource allocation, and scheduling. Optimization and mathematical programming are often employed in these contexts.

Five Crucial Factors When Selecting AI for Production Scheduling

Production scheduling involves making optimal choices to coordinate resources, tasks, and time to meet production goals. It requires handling well-defined parameters and constraints, along with specific objectives like maximising throughput or achieving on-time delivery. As such, it is best suited to rigorous and well-structured AI methods that focus on optimal and feasible decision-making such as mathematical programming. 

Nevertheless, good production scheduling can involve some aspects of learning and reasoning as well. Learning can be useful when some of the parameters are not well defined or static. For example, estimating transfer times between different locations of a fab may depend on various parameters, necessitating the use of a prediction model that has learned from past data. In terms of reasoning, a good decision-making approach should allow some degree of introspection from the user. Contrary to black box approaches, such as deep neural networks, mathematically formal methods such as Mixed Integer Linear Programming (MILP) enable transparency and explainability.

Choosing the right AI technique for production scheduling in semiconductor manufacturing involves navigating the intricate balance among five crucial characteristics, each vital in this high-stakes field:

Optimality refers to the ability of an AI technique to reach and prove that the true optimal solution has been found. In a complex environment such as a semiconductor fab, where small improvements can have significant cost or time implications, optimality is of paramount importance. 

Feasibility is about ensuring that the solution found truly abides by the constraints of the problem. Semiconductor fabs are bounded by many constraints, including machine capacity, human resources, and time windows. An AI solution must respect these constraints while optimizing the schedule. 

Speed is crucial as it directly impacts the responsiveness of the system. Semiconductor manufacturing is a dynamic environment with constantly changing states. Therefore, the selected AI technique must be able to provide fast and accurate solutions to adapt to these changing conditions. 

Explainability refers to the ability of an AI technique to provide insights into how it arrived at a given solution. In a high-stakes environment like a semiconductor fab, explainability helps build trust in the system, enables troubleshooting, and allows for more effective human-AI collaboration.

Flexibility refers to the technique’s applicability across a wide range of possible scenarios and system changes. This attribute highlights the capability of an AI method to be fully autonomous and require  minimal human supervision and intervention. Within the context of a semiconductor plant, this quality is indispensable, especially as complexity grows and specialised personnel are spread thinner across other functions. 

Different AI techniques fare differently on these dimensions. Rule-based systems offer high explainability and feasibility but may lack optimality, especially in complex scenarios. Unforeseen changes in a fab’s state may require rule adjustments or even entirely new ones, affecting flexibility. Heuristic approaches can provide acceptable solutions quickly, but typically cannot provide optimality or feasibility guarantees. Reinforcement learning can potentially offer high levels of optimality and speed, but at the cost of explainability, the risk of infeasibility, and the need for extensive tuning. 

In contrast, mathematical programming techniques, such as MILP, can offer an excellent balance. They provide guaranteed feasibility, while the distance to true optimality can be easily computed. They offer explainability in terms of how decisions are made based on the objective function and constraints. Although computational complexity can be an issue, they can greatly benefit from advanced decomposition methods, and are well complemented by heuristic methods [10].

In the context of semiconductor fab scheduling, where feasibility, optimality, and explainability are particularly important, mathematical programming techniques can be a superior choice for AI implementation. Their deterministic nature and the rigour of their mathematical foundations make them a highly reliable and robust choice for such high-stakes, complex operational problems.

Going beyond with AI
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Today, AI in semiconductor manufacturing stands at a critical point. With the increasing complexity of semiconductor processes and the escalating demand for efficiency and quality, the need for effective AI solutions has never been greater. As evidenced in many large companies’ roadmaps, AI is regarded as a key enabling technology of the future [11]. Companies that do not devote resources to a comprehensive AI strategy risk being left behind.

As we delve deeper into the era of AI-driven manufacturing, the nuanced roles of different AI techniques will become more and more apparent. Machine learning approaches bring novel capabilities for learning and predicting from data: yield improvement and predictive maintenance are very promising paths. When it comes to autonomously and reliably scheduling and planning operations in a fab, an exact optimization approach, such as MILP, becomes the key to unlocking peak performance.
 

‍Authors:
Ioannis Konstantelos, Principal Optimization Engineer at Flexciton
Dennis Xenos, CTO and Cofounder at Flexciton

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References

[1] McKinsey & Company, Scaling AI in the sector that enables it: Lessons for semiconductor-device makers, April 2021. Link

[2] Mönch, L., Uzsoy, R. and Fowler, J.W., 2018. A survey of semiconductor supply chain models part I: semiconductor supply chains, strategic network design, and supply chain simulation. International Journal of Production Research, 56(13), pp.4524-4545.

[3] Lee, T.E., Kim, H.J. and Yu, T.S., 2023. Semiconductor manufacturing automation. In Springer Handbook of Automation (pp. 841-863). Cham: Springer International Publishing.

[4] Mehrdad Mohammadi, Stephane Dauzeres-Peres, Claude Yugma, Maryam Karimi-Mamaghan, 2020, A queue-based aggregation approach for performance evaluation of a production system with AMHS, Computers & Operations Research, Vol. 115, 104838, https://doi.org/10.1016/j.cor.2019.104838

[5] Çınar, Z.M., Abdussalam Nuhu, A., Zeeshan, Q., Korhan, O., Asmael, M. and Safaei, B., 2020. Machine learning in predictive maintenance towards sustainable smart manufacturing in industry 4.0. Sustainability, 12(19), p.8211.

[6] Ishida, T., Nitta, I., Fukuda, D. and Kanazawa, Y., 2019, March. Deep learning-based wafer-map failure pattern recognition framework. In 20th International Symposium on Quality Electronic Design (ISQED) (pp. 291-297). IEEE.

[7] Dreyfus, P.A., Psarommatis, F., May, G. and Kiritsis, D., 2022. Virtual metrology as an approach for product quality estimation in Industry 4.0: a systematic review and integrative conceptual framework. International Journal of Production Research, 60(2), pp.742-765.

[8] Moyne, J., Samantaray, J. and Armacost, M., 2016. Big data capabilities applied to semiconductor manufacturing advanced process control. IEEE transactions on semiconductor manufacturing, 29(4), pp.283-291.

[9] Max Tegmark, Life 3.0, Being human in the age of Artificial Intelligence, 2018 

[10] S. Elaoud, R. Williamson, B. E. Sanli and D. Xenos, "Multi-Objective Parallel Batch Scheduling In Wafer Fabs With Job Timelink Constraints," 2021 Winter Simulation Conference (WSC), Phoenix, AZ, USA, 2021, pp. 1-11, doi: 10.1109/WSC52266.2021.9715465.

[11] Bosch, Humans and machines team up in the factory of the future, October 2021. Link

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Meet Nitin, our Senior DevOps engineer and security guru. Keep reading to learn a bit more about him and what it's like to work in DevOps at Flexciton.

Tell us what you do at Flexciton?

I’m a Senior DevOps engineer in the Platform Engineering Team (PET), which involves building highly available, scalable infrastructure to support various customers deployments, building infrastructure as code and supporting existing environments. I also have an important role to play as a Security Lead, to ensure Infrastructure and Application development follows standard security principals, dealing with Security incidents/threats and resolving them.

What does a typical day look like for you at Flexciton?

A typical day starts with looking at my slack channels to see if there are any issues with infrastructure or customer environments, and checking high priority security incidents raised by our systems. After that we have a scrum meeting to discuss how we are dealing with current tasks, any hurdles and get ready for another challenging day. If I have a dedicated security day then I would be looking at our security board in SecureFrame and begin fixing various failing security tests as we aim to soon get our SOC2 certificate. Also, looking at our SIEM dashboard, check security threats and build smart alerts to help us capture issues beforehand. If I am on DevOps tasks then I will be helping the PET team with building infrastructure for new customers, getting best practices set, and making sure that our development team can build infrastructure.

What do you enjoy most about your role?

What I enjoy most about my role at Flexciton is the variety of tasks and responsibilities that come with being a Senior DevOps and leading the Security work. As we are aiming for a SOC2 certification, I love the challenges I am facing, the various ways I need to consider before making infrastructure changes, and keeping myself always on top of security incidents to make sure I am not missing anything. 

From DevOps point of view, I really enjoyed working on the various initiatives/tech debts including logical grouping of infrastructure, and validation of Azure resources like why/when/how we will use them.

If you could summarise working at Flexciton in 3 words, what would they be?

Grit, innovation, challenges. 

What career advice would you give to your younger self? 

“Never settle down”.

Keep pushing yourself.

If you could swap jobs with anyone for a day, who would they be and why?

I’d love to be an Astronaut. Watching our planet and enjoying the beautiful views of the galaxy. It wouldn't be easy to acquire the skills I'd need, but given a chance I'd give it a try!

Tell us about your best memory at Flexciton?

My favourite memory was when we recently celebrated the 7th anniversary of Flexciton on a boat. We floated around the Thames and enjoyed the lovely views across the river.  

Meet Sully, the Bucket Brigade team's backend wizard, as he shines in the spotlight for July's edition of The Flex Factor. Discover more about the diverse challenges he tackles during his day-to-day and the valuable career advice he wishes he had known earlier.

Tell us what you do at Flexciton?

I’m the Bucket Brigade team's backend developer, whereas the others are optimisation engineers, a frontend developer, a product owner, and some riff raff. Though it’s not a hard separation, this means I tend to do the backend work for our team that isn’t very optimisation focused.

What does a typical day look like for you at Flexciton?

Every day starts off with standup during which we are entertained by bad puns by our team scrum lord, Charlie, and acquire strange German words as sprint names from our German team member, Jannik. During stand up, I often say that I think I'll get something done that day, but then have to say I'm not done with it yet at least one additional morning. The rest of the day usually consists of working solo, doing some code reviews, and not going to too many meetings, unlike some colleagues who've made poor life choices and have frequent meetings. I usually leave between 6 and 7 PM, which is okay because I roll into the office pretty late every morning. I also make great use of the free snacks and colas. 

What do you enjoy most about your role?

I like that we have a variety of different kinds of problems to solve. It's engaging and there are many things we need to do and improve so there are always ways to find new challenges.

If you could summarise working at Flexciton in 3 words, what would they be?

Live. Laugh. Optimize (with a z).

What career advice would you give to your younger self? 

Focus on skills that will follow you from role to role and across companies, rather than company or product-specific skills and knowledge.

If you could swap jobs with anyone for a day, who would they be and why?

I’d maybe swap with a fighter pilot. I feel like on the day I’m there I could improvise and manage to get up in the air, have fun, and figure out how the ejector seat works. Since I’m gone the next day I won’t have to deal with the consequences.

Tell us about your best memory at Flexciton?

I had a lot of fun in Albufeira. Though my memory is hazy, I’m pretty sure it was lots of fun. If I have that memory in my subconscious somewhere I bet it is good

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