Greek Cross

Greek cross is a sheet resistance measurement pattern — a symmetric four-point probe structure shaped like a plus sign (+), providing more accurate sheet resistance measurements than Van der Pauw structures through improved geometry.

What Is Greek Cross?

• Definition: Plus-shaped (+) test structure for sheet resistance measurement.
• Design: Four arms of equal length extending from central square.
• Advantage: Symmetric geometry improves measurement accuracy.

Why Greek Cross?

• Accuracy: Symmetric design reduces measurement errors.
• Repeatability: Consistent geometry improves reproducibility.
• Standard: Widely adopted in semiconductor industry.
• Simple Analysis: Straightforward resistance calculation.

Greek Cross vs. Van der Pauw

Greek Cross: Symmetric, more accurate, requires specific geometry.
Van der Pauw: Works for arbitrary shapes, less accurate.
Preference: Greek cross preferred when space allows.

Measurement Method

1. Current Injection: Apply current through opposite arms.
2. Voltage Measurement: Measure voltage across other two arms.
3. Resistance: R = V / I.
4. Sheet Resistance: R_s = (π/ln2) × R × correction factor.

Design Parameters

Arm Length: Typically 10-100 μm.
Arm Width: Typically 1-10 μm.
Central Square: Small compared to arm length.
Symmetry: All four arms identical.

Applications: Sheet resistance monitoring of doped silicon, silicides, metal films, polysilicon, transparent conductors.

Advantages: High accuracy, good repeatability, symmetric design, standard method.

Limitations: Requires specific geometry, larger than Van der Pauw, sensitive to arm width variations.

Tools: Four-point probe stations, automated test systems, semiconductor parameter analyzers.

Greek cross is the preferred sheet resistance structure — its symmetric geometry provides superior accuracy compared to arbitrary Van der Pauw shapes, making it the standard for semiconductor process monitoring.