4H-SiC Prime vs Test Grade Wafers for Next-Gen Power Devices 

1) What Really Changes Between Prime and Test Grade 4H-SiC?

Prime and Test grades are typically the same base material system, but they are sorted and specified differently. Prime (device/production) grade is selected for lower defectivity, better geometry control, and cleaner epi-ready surfaces. Test grade allows higher defect levels and more cosmetic variation at a lower price, while still being representative enough for meaningful process development.

For example, the document highlights that on 6-inch wafers, typical Prime grades can cap micropipe density to a low single-digit range per cm², while Test lots may allow significantly higher levels. That difference may not matter for tuning an etch step, but it can matter a lot for high-voltage die where defects reduce yield and increase reliability risk.

2) Defectivity Basics: Micropipes, Dislocations, and Why They Matter

When people compare 4H-SiC Prime vs Test grade, defectivity is usually the first concern. Micropipes and dislocation-related defects can act as leakage paths and field hot spots in high-voltage devices. As device voltage class increases, the tolerance for defect-driven failures drops quickly.

A practical way to use grade selection is to match defect budgets to risk: use Test material where the goal is to learn the process window, and reserve Prime lots for multi-layer device stacks, qualification runs, and reliability studies where field failures are expensive.

3) Geometry and Flatness: Warp, Bow, LTV, and TTV

In power device manufacturing, geometry affects more than handling. Flatness and thickness control influence lithography focus windows, uniformity in epitaxy, and repeatability in metrology. Prime grade wafers generally carry tighter limits on:

• Warp (overall shape variation across the wafer)
• Bow (curvature relative to a reference plane)
• LTV (local thickness variation)
• TTV (total thickness variation)

The document provides examples of typical Prime-grade targets on 6-inch material (such as low-micron warp and tighter thickness variation budgets), because these specifications directly affect high-voltage device uniformity and yield.

4) Surface Finish and Epi-Ready Requirements

Surface finish is not just cosmetic in 4H-SiC. Epitaxy quality, defect propagation, and interface behavior can depend on surface preparation. Prime grade wafers are typically specified with epi-ready polish/CMP standards and tighter surface roughness targets.

Test grade material may still be chemically representative, which is exactly why it’s useful for deposition tuning, etch development, and cleaning/anneal recipe validation. But for final devices, surface-related defects can impact yield and long-term reliability.

5) When Test Grade 4H-SiC Is the Smarter Choice

Test grade is often the best choice when learning is the priority and yield is not the key outcome. Typical “Test grade” use cases include:

• Tool installation and baseline qualification
• Deposition and etch recipe development
• Metrology method development (thickness, roughness, bow/warp)
• Implant and anneal trials before committing Prime inventory
• Training runs and process monitoring lots

Many programs start with Test grade to build stable process windows, then transition to Prime as soon as the flow becomes production-representative.

6) Diameter Scaling: 100mm vs 150mm vs 200mm

Diameter changes the economics of grade decisions. At smaller diameters, Test grade is a common way to start because total wafer spend is lower and the number of die at risk is smaller. As programs scale to 150mm and 200mm, defects and flatness have a larger impact on cost per usable die.

A typical scale-up strategy is: use Test grade for early learning at 100mm or limited 150mm lots, then standardize on Prime or near-production material for 150mm/200mm qualification and high-reliability device runs.

7) Why Most Programs Focus on 4H-SiC (vs 6H-SiC)

Although both 4H and 6H polytypes exist, many modern power and RF programs standardize on 4H-SiC because it offers a strong balance of mobility and breakdown performance. That’s why Prime vs Test grade distinctions are especially important in 4H-SiC: the target applications are demanding and the cost of field failures is high.

8) U.S. Sourcing and Cost Strategy in a Tariff-Sensitive Market

For U.S.-based manufacturing and R&D programs, wafer procurement is part of risk management. Prime 4H-SiC wafers—especially in larger diameters—represent a major cost line item, and tariffs or logistics can amplify that premium. Many teams reduce total program cost by blending grades:

• Test grade for equipment qualification, single-layer experiments, and monitoring
• Prime grade for final device stacks, qualification, and reliability lots

This mixed-grade approach keeps learning fast without sacrificing the integrity of device-level results.

9) Practical Checklist: Choosing Prime vs Test Grade 4H-SiC

A simple way to choose a grade is to answer three questions:

1. Are devices from this lot intended for final performance reporting or shipment?
2. Is yield critical to the program’s economics or schedule?
3. Does this run need to represent the full production process-of-record?

If you answer “yes” to all three, Prime grade is typically the safer choice. If the goal is process learning, tool setup, or monitoring, Test grade is usually the cost-effective path.

Conclusion

Prime vs Test grade 4H-SiC selection is ultimately about aligning material quality with device risk, budget, and schedule. Prime grade supports high-yield, high-reliability power devices with tighter defect and geometry control. Test grade enables fast process development and tool qualification without tying up expensive Prime inventory. If you share your target diameter, voltage class, and application, we can recommend a practical grade mix for your program.