Many semiconductor companies today are focused on successfully delivering products to their customers while also reducing their environmental footprint through a range of initiatives including water recycling, renewable energy use, reduced emissions, and efficient building design. In addition, chip manufacturers employ continuous improvement programs to optimize their operations and work with their supply chain to directly reduce the resources used in fabs.
To produce chips, semiconductor fabs start with silicon wafers or other substrates (e.g., SiC, GaN, GaAs, sapphire, etc.) and precisely add and subtract specialized materials, creating nanoscale patterns that form the transistors and connectors that determine the chips’ functions. Depending on the complexity of the process technology, it can take 10 to 15 weeks from the time a wafer enters a fab until processing is complete, during which time it may pass through up to one thousand process steps. Each step involves process tools and materials that must meet rigorous quality standards to ensure that the resulting chips are functional, reliable, and meet power and performance specifications. If something goes wrong at a single process step, it can cause lower performance, functional inconsistencies, or outright failure of the chips. Chips that do not meet quality standards are scrapped.
Because chip manufacturing requires energy, wafers, chemicals, and other resources, from an environmental perspective, it’s imperative to ensure that all process steps meet stringent quality standards to prevent wafer scrap and reduce wafer rework. That’s where process control comes in – inspection and metrology systems measure the wafers after process steps and look for problematic defects or variations that can cause chip performance, reliability, or other quality issues. Identifying process issues early allows fabs to take quick corrective action, reducing scrap and rework – and ultimately, reducing resource consumption.
Fabs looking for creative ways to further reduce environmental impact are upgrading their process control solutions to be more capable and are also adding additional inspection and metrology steps. These process control green schemes reduce scrap and net resource consumption per good die out.
Green Scheme 1: Improved Process Control Performance
Process control provides the data necessary for fab engineers to make production wafer dispositioning decisions and to address process issues. For example, if after-develop inspection (ADI) data indicate a high number of bridging defects on patterned wafers following a particular lithography patterning step, the lithography engineer takes several corrective actions. In addition to sending the affected wafers back through the litho cell for rework, the engineer may stop production through the litho cell to fix the underlying process issue. These actions limit the amount of material impacted and potentially scrapped.