Laser risk assessment and local rules: laser-diode modules for semiconductor analysis
Research group and location
Security Group “Tamper Laboratory”, Room SE09 (William Gates Building)
Description of product and application
An assorted collection of laser-diode modules and laser diodes is being kept on stock. They are intended for use in experiments to investigate how laser irradiation of micrometer-sized patches of a decapsulated semiconductor chip (e.g., microprocessor or programmable-logic device) can be used to probe and interfere with the operation of the circuit, and how practical it is to use laser diodes this way to bypass security controls implemented on the chip.
Description of the lasers
List of available laser-diode modules and replacement laser diodes (from ~sps32/laser_list.txt):
Model Manufacturer Wavelength Power Supply Comments ---------------------------------------------------------------------------- BBT-60MW AixiZ 473nm 60mW 240VAC TTL/Analog Laser pointer China 532nm 5mW 2xAAA Focusable Laser pointer China 532nm 7mW 2xAAA HLM1200-532-5 AixiZ 532nm 5mW 3VDC 5 min 51G30 China 532nm 30mW 240VAC TTL control LM-532-35 OEM 532nm 35mW 3VDC 5 min damaged G532-50EC China 532nm 50mW 240VAC TTL control GBS-60 xplalaser.com 532nm 60mW 240VAC TTL control HLM-G2244116-A AixiZ 532nm 120mW 240VAC TTL control PPM25/5638 Power Technology 639nm 25mW 12VDC PPM25/5638 Power Technology 639nm 25mW 12VDC HLM1230-635-5 AixiZ 635nm 5mW 3.2VDC HLM1230-650-5 AixiZ 650nm 5mW 5VDC HLM1230-650-5 AixiZ 650nm 5mW 5VDC RLDH660-40-3 Roithner 650nm 40mW 3VDC Focusable HLM1230-650-100 AixiZ 650nm 100mW 3.2VDC 5 min HLM1850-655-100 AixiZ 655nm 100mW 3.2VDC IQ1A60_658-70G2 Power Technology 658nm 60mW 5-12VDC Focusable/Analog IQ1A60_658-70BG2 Power Technology 658nm 60mW 5-12VDC Focusable/Analog 9517065 Melles Griot 670nm 1mW 5VDC 9517071 Melles Griot 670nm 1mW 5VDC Laser pointer China 670nm 2mW 5VDC 56-DLB-102/P Melles Griot 670nm 3mW 5VDC 56-DLB-102/P Melles Griot 670nm 3mW 5VDC LT022MC Sharp 780nm 5mW 45mA OEM LT022MC Sharp 780nm 5mW 45mA OEM LT022MC Sharp 780nm 5mW 45mA OEM LT022MC Sharp 780nm 5mW 45mA OEM 51285 Melles Griot 830nm 24mW 12VDC LDM830/40LT Roithner 830nm 40mW 5VDC Focusable IQ1H75_1060-100G2 Power Technology 1060nm 75mW 5-12VDC Focusable/TTL IQ2A75_1060-150G2 Power Technology 1060nm 75mW 5-12VDC Analog IQ2A75_1060-150G2 Power Technology 1060nm 75mW 5-12VDC Analog IQ2A35_1080-80G2 Power Technology 1080nm 35mW 5-12VDC Analog IQ1A07_1310_10G2 Power Technology 1310nm 7mW 5-12VDC Analog IQ1A07_1310_10G2 Power Technology 1310nm 7mW 5-12VDC Analog PDM-1064 Alphanov 1060nm 300mW 240VAC TTL control Diode Manufacturer Wavelength Power Size Comments -------------------------------------------------------------------------- QL63D5SA Roithner 635nm 5mW 5.6mm S RLT6305G Roithner 635nm 5mW 9mm S RLT6505G Roithner 650nm 5mW 9mm S SLD65018260 Roithner 650nm 5mW 5.6mm S ADL65401T4 Roithner 650nm 40mW 5.6mm S 60C ADL65401T4 Roithner 650nm 40mW 5.6mm S 60C RLT6550G Roithner 650nm 50mW 9mm M RLT6550G Roithner 655nm 50mW 9mm M ADL66501TL Roithner 660nm 50mW 5.6mm S ADL66501TL Roithner 660nm 50mW 5.6mm S ADL66502TL Roithner 660nm 50mW 5.6mm S 60C ADL66502TL Roithner 660nm 50mW 5.6mm S 60C RLT6650G Roithner 660nm 50mW 9mm M RLT66100G Roithner 660nm 100mW 9mm M RLT66200G Roithner 660nm 200mW 9mm M RLT6705MG Roithner 670nm 5mW 5.6mm S RLT6705G Roithner 670nm 5mW 9mm S RLT7830MG/60116 Roithner 780nm 30mW 5.6mm S ML601J24-01 Mitsubishi 787nm 60mW 5.6mm S RLT80820G Roithner 808nm 20mW 9mm S HL8318G Roithner 828nm 30mW 9mm S RLT8330G Roithner 830nm 30mW 9mm S ELD83NPT50 Roithner 830nm 60mW 9mm S RLT8520MG Roithner 850nm 20mW 5.6mm S RLT8750G Roithner 870nm 50mW 9mm S RLT904-20G Roithner 904nm 20mW 9mm S RLT9520MG Roithner 950nm 20mW 5.6mm S RLT9820MG Roithner 980nm 20mW 5.6mm S L98T50M Roithner 980nm 50mW 9mm M L98T50M Roithner 980nm 50mW 9mm M RLT98500GOP Roithner 980nm 500mW 9mm M RLT981000G Roithner 980nm 1000mW 9mm M RLT1020-500G Roithner 1020nm 500mW 9mm M LD-10s-1060 QPhotonics 1065nm 10mW 9mm S RLT1060-10MG Roithner 1060nm 10mW 5.6mm S LD-50s-1060 QPhotonics 1065nm 50mW 9mm S QLD1060-100s QPhotonics 1065nm 100mW 9mm S QLD1060-200s QPhotonics 1065nm 200mW 9mm S QLD1080-100s QPhotonics 1080/1095nm 100mW 9mm S RLT1300-20G Roithner 1310nm 20mW 9mm S QLD1300-50s QPhotonics 1310nm 50mW 9mm S
The currently available laser-diode modules cover visible and infrared wavelengths in the range 532–1310 nm. They can all be operated continuously, but may also be operated from a manually- or computer-controlled pulsed current source.
In addition to normal lab power supplies, two specialized laser-diode power supplies are available to drive laser modules and diodes with controlled power levels:
- ILX Lightwave LDP-3811 precision pulsed current source
- Newport Modular Controller, Modell 8000, with the
following driver modules installed:
- Module 8505: 500 mA Laser Diode Driver (LDD)
- Module 8560: 6000 mA Laser Diode Driver (LDD)
- Module 8605: 500 mA LDD / 2.5 A TEC
- Module 8350: 5 A Temperature Controller (TEC)
An OMM-6810B optical multimeter is available to characterise the wavelength and power of a laser diode setup.
Description of the beam delivery system
When used in experiments, the laser modules are enclosed in a protective housing that prevents access to radiation in excess of Class 1 limits, except for the output beam. These housings are mounted onto one of three ports of a Mitutoyo FS60Y microscope. One of these ports was specifically designed to be used for a laser and is equiped with a safety interlock. A second port was originally designed to house the sensing laser of an auto-focus unit. A third port was installed by the user of the microscope by inserting a beam splitter in the optical path of the microscope and making the necessary mechanical changes to the body of the microscope.
Objective lenses used include:
- Mitutoyo M Plan Apo NUV 50× (working distance 15 mm, NA=0.42)
- Measured diverging beam area 20 mm after focal plane (with maximally opened aperture): about 3×3 mm
- Solid angle of divergence: 0.02 steradians
- Nominal ocular hazard distances (NOHD) from focal area = power /
(solid angle of beam * MPE):
to be determined for specific experimental setup
- Mitutoyo M Plan Apo NIR 100× (working distance 12 mm, NA=0.50)
- Measured beam divergence 20 mm after focal plane (with maximally opened aperture): about 6×6 mm
- Solid angle of divergence: 0.09 steradians
- Nominal ocular hazard distances (NOHD) from focal area = power / (solid angle of beam * MPE):
to be determined for specific experimental setup
The laser beam leaves the microscope vertically downwards and is either absorbed by the target, or reflected back upwards against the microscope, thereby avoiding direct exposure of nearby observers. The NOHDs are of concern if the beam is reflected by some specular (mirroring) surface in its normally only vertical path.
The laser beams are used primarily to lift electrons in an semiconductor to higher energy levels, either to create a photoelectric current across diode junctions, or to influence the channel characteristics and threshold voltage of individual CMOS FET transistors on a circuit. Even though some of the available diodes and driver modules are capable of producing substantially higher power levels, the power levels of particular interest for this application tend to be in the 1-5 mW range. As a result, experiments are usually planned with power levels within the Class 2 safety limits (for visible light).
- Some of the available laser-diode modules and current sources were designed to be capable of outputting Class 3B levels (for short times perhaps even Class 4 levels) according to EN 60825. In the case of an experimental error, where a much higher than intended driving current is used, the beam enclosure fails, and a reflective object below the objective lens deflects the beam from its normally vertical path, the experimental hardware could inflict severe eye damage and (theoretically) even skin damage.
Whom those hazards affect
- The laser is operated only by one researcher, Dr Sergei Skorobogatov.
- A Class 3 laser has the potential of creating eye damage to anyone within viewing range. This includes observers of demonstrations of the laser, other users or visitors of the same laboratory room, people outside in nearby buildings and right outside the door of room SE09.
The experimental setup consisting of the microscope, attached laser diodes, target chips mounted on a 3-axis positioning system, is located in the hardware laboratory (room SE09) of the computer-security research group on the second floor of the William Gates building. This is a dedicated room for experimental work, which is normally locked and to which only selected researchers have access. The room has two windows facing the CAPE building. The single door leading to the corridor has no window. The room is equipped with laser-safety blinds on all windows and provides otherwise the same facilities as any other normal office in the building (white diffusely-reflecting walls, dark carpet). It houses a large amount of electronic and optical test and measurement equipment.
Local rules for safe use
- Experiments involving laser diodes must only to be designed and used by a registered and trained user (currently only Dr Sergei Skorobogatov), in ways agreed with the Departmental Laser Safety Officer.
Safe working procedures and controls
- The operator of a laser-diode module should assume that a Class 4 laser beam might occur (e.g., due to operator error), even if the planned beam intensity for the experiment is within a lower class.
- Avoid direct exposure of any person to the beam or to a reflection of it.
- A laser diode should never be powered up unless it is housed in a protective enclosure or mounted onto a microscope with blocked eye piece.
- On a microscope, laser diodes must only be used with a high magnification (50× or more) objective lens designed for the chosen wavelength. Only then will a reasonably divergent beam leave the enclosure of the microscope.
- The laser diode should automatically deactivate after the end of a measurement and should not be operated unattended. Use of the laser should be suspended by the operator when someone unexpectedly enters the room (e.g., a cleaner emptying the bin).
- Check that the target surface is horizontal. This can be verified through the alignment CCD camera and will ensure that specular beam reflections will mainly be absorbed by the microscope.
- Enclose the beam path, including the area around the objective lens and the laser target. A simple and practical way to achieve such an enclosure without interfering with easy access to the target is to attach opaque black plastic foils (e.g., cut from suitable anti-static bags) to the microscope head, such that they form an opaque curtain around the target.
- If working with an enclosed beam bath is not practical, the laser operator should wear laser safety goggles that are suitable for the wavelength used during the operation of the laser and close the window blinds. Other persons should not be in the room during experiments if there is a possibility that the beam that leaves the microscope exceeds Class 2 safety limits at more than 10 cm distance from the objective lens.
- Safety goggles should be checked for damage before each use.
- The SE09 door should be locked if the room will be empty for more than about 15 minutes.
- A suitable video camera should be used to align the projection of the laser aperture with the target area.
- A suitable laser radiation hazard sign should be posted clearly visible near the system. A suitable xfig design is available in /homes/mgk25/proj/misc/warning-laser-ql.fig.
- A laser radiation hazard sign should also be visible from the outside of the door of room SE09.
- The laser-diode current source, microscope and the metal table on which they are installed must be properly grounded via a protective-earth connection. The impedance of that connection should be verified regularly, in accordance with the department's portable appliance testing (PAT) policy.
Training and reference material
Any user or designer of experiments involving laser diodes must first attend the course Laser Safety for Class 3B and 4 Laser Users and Research Supervisors offered by the Health and Safety Division.
The user should also study the following literature carefully and keep it near the experiment for easy reference:
- Safe Use of Lasers, Occupational Health and Safety Service, University of Cambridge, HSD013R (rev 4), September 2012.
- Long Working Distance Objectives, Datasheet 99MBA113B, Japan.
For questions and further information regarding the safe use of laser diodes, contact the Departmental Laser Safety Officer, currently Dr Markus Kuhn (phone 34676, room GE16).
This assessment was carried out by Markus Kuhn and Sergei Skorobogatov
Date: June 2006, last reviewed May 2013