In our blog: A brief overview of mask shop economics, we discussed many of the challenges of reticle manufacturing, particularly the focus on consistently building and shipping perfect reticles on time. It is essential to track critical milestones within the mask shop to monitor reticle manufacturing efficiency and the ability to meet customers’ timing expectations. The end goal is to ensure high factory efficiency, product quality, and customer satisfaction.
Mask shop milestones can be divided into two main categories: order-centric and manufacturing-centric.
Order-centric
Order-centric milestones focus on the customer’s perspective. A mask’s manufacturing journey begins when a reticle order is received from a customer and recorded within the Manufacturing Execution System (MES) as the Order Received Date. Key customer dates like the Contract Shipping Deadline and the Requested Shipping Deadline arrive with the order and accommodate both contractual obligations and special customer requests based on the specific date the reticle is needed within the wafer fab (commonly referred to as the wafer manufacturing need date). A set of manufacturing specifications also accompanies the order, indicating processing tolerances and limits that ensure the necessary quality of the finished product.
Perhaps the most important item arriving with the reticle order is the design data defining the reticle pattern itself. A reticle data file can be many gigabytes in size, and over a terabyte for advanced masks. Even when transferred over high-bandwidth commercial data networks, mask data transfer can take many hours. This is especially the case if there are multiple, competing data transfers occurring simultaneously. The Order Start Date is recorded when the data transfer is complete and this initiates the order’s cycle time clock. From the customer’s perspective, everything beyond this point is within control of the mask shop. The cycle time clock then ends when the finished reticle is shipped from the mask shop, as recorded by the Order Ship Date.
The mask shop and its customers sometimes disagree about how to measure cycle time. From the customer’s perspective, the cycle time clock should begin when they press the “Go” button to transfer the mask order and start the reticle data transfer and should end when the finished reticle is delivered to their factory.
However, the mask shop can’t control the data transfer time. This is a function of the customer’s reticle data size and, at least partially, of the bandwidth of the customer’s commercial data transfer pipe. The mask shop also cannot control the time it takes a shipper such as UPS or FedEx to physically deliver the reticle to the customer’s factory. Since these are all out of the mask shop’s control, they are out of bounds from a cycle time perspective.
Manufacturing-centric milestones
Manufacturing-centric milestones focus on the mask shop’s manufacturing process – the things within the mask shop’s control.
Once the data transfer from a customer is complete, the data undergoes a process called “fracture,” that converts the raw design data into a format compatible with the mask shop’s patterning tools. The fracture process can also take hours, and its duration is recorded by the Fracture Start Date and Fracture End Date.
Physical processing begins once the fracture process is finished and the fractured data is transferred to the first tool in the manufacturing process, the one that writes the reticle pattern onto a mask blank. However, physical processing rarely begins right away. The reticle must wait until orders received ahead of it have completed processing on the write tool, a period commonly called the Write Queue Time. In mask shops manufacturing advanced masks this step also can last many hours or even days.
Once processing finally begins at the first manufacturing step, the Manufacturing Start Date is recorded and the manufacturing’s cycle time clock starts. From the mask shop’s perspective, everything before this point – data transfer time, fracture time, write queue time – is out of their control and irrelevant in evaluating manufacturing efficiency.
Within the manufacturing lifecycle of each reticle, the Track-In Date and Track-Out Date bookend each step in the process flow, and the Processing Start Date and Processing Complete Date record when physical processing begins and ends within each step.
Once again, a reticle may have to wait for previous reticles to finish processing before it can start. A reticle’s queue time is measured by the time between the Track-In Date and the Processing Start Date. Changes to the average queue time for individual steps in the process flow – the average time reticles wait at a step before beginning processing – can indicate that a specific process step may be a “bottleneck” process. This demands special attention from both the production and engineering staff to ensure tools performing that process remain available and running.
Where the Manufacturing Start Date starts manufacturing’s cycle time clock, the Manufacturing Complete Date marks the completion of physical mask processing and stops the clock. The average manufacturing time – the average time between these – is a critical metric indicating the mask shop’s operational efficiency. The lower, the better.
Finally, the Shipping Deadline – the sooner of the customer-specified Contract Shipping Deadline or Requested Shipping Deadline – defines when a mask must be shipped per the mask shop’s production plan to reach the customer’s factory using their chosen method of shipment. (The Ship Date records when the mask is handed off to the shipper for transport to the customer.)
Monitoring and managing milestones
Monitoring and managing these milestones for each reticle ensures consistent on-time delivery. Furthermore, monitoring these milestones over time is a barometer into a mask shop’s overall health and manufacturing efficiency and can offer key insights into opportunities for improvement.
The Manufacturing Execution System (MES) provides real-time data on manufacturing processes, ensuring that each milestone, as well as other key manufacturing metrics, are accurately recorded and the insights made available to optimize process flows, reduce cycle times, and enhance overall efficiency.
The MES also facilitates communication between everyone within the mask shop, ensuring that everyone is aligned with production goals and timelines to effectively meet customer expectations.
