Semiconductor Inspection And Metrology System Using Laser Pulse Multiplier

A pulse multiplier comprising:

• a first ring cavity including:
• a first beam splitter;
• a set of one or more mirrors;
• and
• a second ring cavity including:
• a second beam splitter;
• and
• a second set of one or more mirrors;
• wherein the first beam splitter directs a first fraction of each input laser pulse to the second beam splitter, and directs a second fraction of each input laser pulse into the first ring cavity, and
• wherein the second beam splitter directs a third fraction of each pulse incident on it to an output of the pulse multiplier, and directs a fourth fraction of energy of each pulse incident on it into the second ring cavity.

A system comprising:

• a pulse multiplier including:
• a beam splitter for receiving a laser pulse;
• and
• a set of mirrors for creating a ring cavity including the beam splitter,
• wherein the beam splitter directs a first fraction of energy of the laser pulse as an output of the pulse multiplier, and directs a second fraction of the energy of the laser pulse into the ring cavity.

A method of generating pulses for a system, the method comprising:

• generating a regular repeating series of laser pulses from a laser;
• optically splitting each laser pulse using a beam splitter and directing a first fraction of the laser pulse to an output and directing a second fraction of the laser pulse into a ring cavity comprising one or more mirrors;
• optically splitting each pulse after it has travelled around the ring cavity so that substantially the second fraction is directed to the output and substantially the first fraction is recirculated around the ring cavity;
• wherein an optical path length of the ring cavity is set so that a time for a pulse to travel once around the ring cavity is approximately equal to an odd integer times half a time interval between the laser pulses and wherein the first fraction and the second fraction are chosen so that output pulses are of approximately equal energy;
• and
• transmitting the output pulses to the system.