Most semiconductor wafers are made of silicon, the second most common element in the Earth’s crust. Yet, silicon’s abundance does not mean that wafers are inexpensive. The pure form of silicon that’s used in semiconductors does not occur naturally and must be refined and mixed with a dopant that alters material properties and electrical characteristics. Silicon ingots are formed, wafers are cut, and more costs are added during subsequent processing steps that include lapping and polishing, thin film deposition, and lithography. This article, the second in a series, considers the costs associated with wafer fabrication and explains why it’s worth inspecting and measuring wafers during each processing step.
At MTI Instruments we make inspection and metrology systems for semiconductor wafers made of silicon, silicon carbide (SiC), germanium (Ge), indium phosphate (InP), and gallium arsenide (GaAS). MTI’s products include Proforma and Digital Accumeasure systems that make non-contact measurements of disc geometry, the subject of the first article in this series. Because MTI’s capacitance-based systems cost significantly less than equipment that is fully automated, our semi-automated and manual solutions provide a faster return on investment (ROI). Moreover, MTI’s inspection and metrology systems can be used at the front end of processing before significant costs are added with lithography. By that point, the amount of waste can be in the thousands of dollars.
The High Cost of Wafer Waste
With each processing step, the costs associated with a wafer increase. According to Wafer Pro, bare discs can range from $27 to $98 (USD). According to Wafer World, $100 to $500 per disc is typical since prime grade wafers cost significantly more than test grade, dummy grade, or reclaimed wafers. Finished semiconductor wafers that combine high performance with high density are even more valuable. As reported by the website Tom’s Hardware, TSMC’s estimated price for a 300 mm wafer at 5 nm is nearly $17,000. In part, that’s because the new N5 technology that TSMC uses to produce these wafers requires significant capital expenditures (CapEx).
The Tom’s Hardware estimate far exceeds the approximately $9500 that TSMC charges for a 300 mm wafer patterned with N7 technology. The company also sells 300 mm wafers at 16 nm or 12 nm for about $4,000. Regardless of their sales price, any of these finished wafers has incurred much greater costs than a cut and polished disc. Whether it’s for older designs that use existing manufacturing technologies or newer wafers made with next-generation nodes, the semiconductor industry risks adding expensive waste by failing to inspect wafers before subsequent processing occurs. Simply put, it’s better to discard a $100 bare disc than a $4,000, $9,500, or $17,000 finished wafer that’s been patterned and packaged.
Wafer Sizes, Fabrication Costs, and Rates of Increase
Because CapEx takes years to depreciate, the cost per square inch of silicon is at its highest whenever a new wafer size is introduced. Costs per square inch decrease over time, but there are also higher fabrication costs with larger wafer diameters. In an article for SEMI called The Macroeconomics of 450 mm Wafers, Apek Mulay writes that “for every succeeding increase in wafer size, there is approximately a 1.4 increase in costs of manufacturing.” Therefore, companies that process wafers in the world’s most popular size, 300 mm, already have higher fab costs than processors of 125 mm or 200 mm discs.
For wafers in all sizes, the semiconductor industry can also expect to pay higher fabrication costs over time. In a report from the Center for Security and Emerging Technology (CSET), authors Saif M. Khan and Alexander Mann write that “the highest-value sectors”, which include semiconductor fabrication, “have seen especially steep rates of cost growth”. Since the early 2000s, fab costs have risen at over 10% per year. The CSEET report, AI Chips: What They Are and Why They Matter, also warns that “as semiconductor complexity increases, demands for high-end talent drives fabrication cost overruns”. Fixed costs pose high barriers to entering the industry, but variable costs are squeezing the profits of existing players.
Cost-Effective Wafer Inspection and Measurement
The third and final article in this series from MTI Instruments compares three types of wafer inspection and measurement systems: fully automatic, semi-automatic, and manual. The article also describes the benefits of MTI’s Proforma 300iSA, a semi-automated system, and MTI’s Profoma 300i, a manual system, for measuring disc geometry. As the Application Notes section of our website shows, MTI Instruments has deep experience serving the semiconductor industry. For more information about our capacitance-based solutions for wafer inspection and measurement, contact us.