Computer Laboratory

Risk assessments

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.

Laser process

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).

Identified hazards

  1. 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.

Environment

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

User

  • 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.

Signage

  • 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.

Electrical safety

  • 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:

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