Process Control Monitor (PCM) — test structures placed in the scribe lines between dies that are measured to verify each process step is within specification, providing statistical process control across every wafer.

What PCM Structures Measure

• Transistor parameters: $V_{th}$, $I_{on}$, $I_{off}$, leakage, breakdown voltage
• Resistors: Sheet resistance of each implant layer, metal layers, poly, contacts
• Capacitors: Gate oxide capacitance (thickness), inter-metal capacitance
• Diodes: Junction leakage, breakdown voltage
• Alignment marks: Overlay accuracy between layers
• Ring oscillators: Dynamic speed measurement (actual circuit speed)

Where They Are

• Scribe lines: The 50–100μm wide lanes between dies that are cut during dicing
• Drop-in cells: PCM blocks scattered within the die itself (between functional blocks)
• Scribe line structures are destroyed during dicing — their measurement data is already captured

Measurement Flow

1. After each critical process step, measure PCM structures on sample wafers 2. Data feeds into Statistical Process Control (SPC) charts 3. If parameters drift outside control limits → stop production, investigate 4. Wafer-level acceptance: Only wafers with PCM data within spec proceed

PCM data is the earliest indicator of process health — it catches problems hours or days before functional testing would reveal them.