4-point Probe

About

Signatone 4-point Probe with HP 34401A Multimeter in Metrology Bay

Process: This is a manual 4-point probe system used to measure sheet resistance (Rs) and calculate resistivity (ρ) of thin films, doped layers, or bulk materials non-destructively. The four-point configuration eliminates contact resistance errors, providing accurate electrical characterization of conductive layers.

Hardware: Signatone SP4 probe head with four in-line or square-arranged tungsten tips (typically 1 mm spacing). Manual or semi-automatic probe placement on sample. Readout via Hewlett Packard (HP/Agilent) 34401A digital multimeter for voltage/current measurement. Probe force adjustable for consistent contact.

Key Features:

• Probe configuration: In-line or square 4-point
• Measurement range: From mΩ/sq to MΩ/sq (depending on film thickness and material)
• Accuracy: High (limited mainly by probe spacing calibration and sample uniformity)
• Readout: HP 34401A multimeter (high precision, 6½ digit resolution)
• Sample size: Flexible (small pieces to full wafers; probe head movable)

Applications:

• Sheet resistance mapping of deposited metals (Au, Al, Ti, etc.)
• Resistivity measurement of doped semiconductors (Si, GaAs, etc.)
• Quality control of transparent conductors (ITO, AZO)
• Monitoring implant/diffusion doping levels
• Thin-film thickness estimation (if resistivity known)
• Process development and failure analysis

Usage: Place sample on stage, lower probe head to contact surface, apply current through outer probes, measure voltage across inner probes, read resistance on multimeter. Use correction factors for finite sample size/geometry if needed. Average multiple points for uniformity.

Detailed Specifications

• Model: Signatone SP4 probe head + HP 34401A multimeter
• Location: Metrology Bay
• Probe spacing: Standard 1 mm (confirm on tool)
• Measurement type: DC 4-point probe (sheet resistance Rs in Ω/sq)
• Readout: HP 34401A digital multimeter (high precision voltage/current)
• Features: Manual probe placement, adjustable probe force, non-destructive
• Restrictions: Requires conductive surface; avoid damaging soft/delicate films; calibrate probe spacing periodically
• Other: Simple, reliable tool for quick electrical characterization in cleanroom

Documentation

• HP 34401A Multimeter SOP
• Training required – contact lab staff (Chandan Ramakrishnaiah or Shivakumar Bhaskaran)

Recipes & Data

• Standard Measurements: Common setups include:

 * Thin metal films (e.g., Au, Al): Rs typically 0.1–10 Ω/sq
 * Doped Si layers: Rs 10–1000 Ω/sq depending on doping
 * ITO transparent conductors: Rs 10–100 Ω/sq

• Process Control: Take multiple points across wafer for uniformity map. Use van der Pauw method for non-square samples if needed. Convert Rs to resistivity ρ = Rs × thickness (thickness from ellipsometer/profilometer).
• Notes: Ensure good probe contact (clean tips if needed). Apply low current to avoid Joule heating in thin/high-resistance films. Record probe spacing calibration factor.

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