Optical Beam Induced Resistance Change (OBIRCH)

Features

OBIRCH is a technique for determining the size and locating of defects by utilizing the fact that the resistivity changes due to the heating of the defective locations. Local heating is accomplished by laser irradiation. The following items can be identified and localized:

• Voids and precipitates in wires and vias

• Abnormal contact resistance

• Wiring short circuits

• DC current path

• Minute current leakage in gate oxide.

Examples of devices

• Si transistors and devices such as metal-oxide semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), and complementary MOS (CMOS) image sensors.

• Power semiconductor devices, such as SiC Schottky barrier diodes and MOSFETs.

• Light-emitting GaInAlN devices such as laser diodes (LD), and light-emitting diodes (LEDs)

• High-electron mobility transistors (HEMTs) such as GaN and GaAs transistors

• Micro electro-mechanical system (MEMS) devices such as pressure sensors and accelerometers

Principle of operation

A laser beam is scanned across the area to be observed as shown schematically in Figure 2.The temperature of the laser-irradiated portion then increases and thus also the resistance. The voltage (or current) is then recorded synchronously with the laser scan as shown by (2) in Figure 2, and the change in voltage is calculated as

	\[\mathrm{\Delta}V \cong - \frac{\mathrm{\Delta}R}{R}I\]	(1)
	\[\mathrm{\Delta}R \propto \mathrm{\Delta}T,\ \mathrm{\Delta}T_{\text{CR}}\]	(2)

Here, \(I\) is the wire current, \(R\) the wire serial resistance, \({\mathrm{\Delta}T}_{\text{CR}}\) the thermal coefficient of resistance, \(\mathrm{\Delta}T\) the temperature change, and \(\mathrm{\Delta}I\) and \(\mathrm{\Delta}R\) the beam-induced current and resistance change, respectively. \(\mathrm{\Delta}R\) depends on the type of defects such as voids and precipitates and are detected as changes in the measured current (or voltage) which are not related to \({\mathrm{\Delta}T}_{\text{CR}}\).

Data examples

Data delivery formats

• Raw image data (8-bit grey, \(256 \times 256\)): TIFF file, JPEG on request

• Image data (TIFF, JPEG) with annotations (sample name, measurement conditions, and magnification (scale bar).

Measurement specifications

Property	Value	Unit	Notes
Maximum sample diameter	150	mm
Maximum sample height	50	mm
Measurement area	0.26×0.26	mm	\(\times 50\) magnification
	0.65×0.65	mm	\(\times 20\) magnification
	2.6×2.6	mm	\(\times 5\) magnification
	13×13	mm	\(\times 1\) magnification
Probe Position accuracy	~2	mm	Laser spot diameter \(1.3\mu\text{m}\)
Laser modulation frequency	5 or 20	kHz	S/N ratio improved by using lock-in amplifier
Electrical probe tip radii	1, 7, 30	µm
Applied DC voltages	\[\pm 25\]	V	100 µA current
	\[\pm 10\]	V	100 mA current

Items for enquiries

• Purpose and scope of the analysis

• Sample information:

  1. Quantity, availability of pre-analysis samples

  2. Positions of the electrical probes, maximum voltage, dominant charge carrier (p or n), substrate material and thickness (for back-side OBIRCH), I-V characteristics

  3. Care instructions

• Delivery date:

  1. Desired delivery dates of preliminary and final results

  2. Handling instructions

• Other relevant information

Caution

The following materials have a negative effect on the measurement.

• Devices where current and voltage become unstable due to laser irradiation.

• Samples damaged by laser irradiation.

• Samples that do not make ohmic contact with the probes.