CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 10/114,337, filed Apr. 1, 2002, now U.S. Pat. No. 6,734,387, which is a continuation in part of Ser. No. 09/321,499, filed May 27, 1999, now U.S. Pat. No. 6,373,565, issued Apr. 16, 2002.

BACKGROUND

1. Field of the Invention

This invention relates generally to UV and visible laser systems, and their methods of use, and more particularly to UV and visible laser systems that are suitable for semiconductor inspection or processing.

2. Description of Related Art

An increasing number of laser applications in the semiconductor industry require UV or visible laser light. These applications include inspection as well as materials processing tasks. Many of these applications require that the sample under test be kept clean or be in close proximity to processing equipment, and thus the entire machine is located in a clean room environment.

Diode-pumped solid-state lasers are finding increasing acceptance in this market because of their robustness. These systems consist of several subsystems: a power supply to run the pump diodes, the pump diodes themselves, the laser head, and a harmonic conversion device to generate the visible or UV radiation. Typically, the entire laser system is included within the semiconductor-processing machine, which is located in the clean room.

Diodes used as the pump source can be positioned in the power supply. Pump light is then coupled from the diodes in a multi-mode fiber, and is conveyed to the laser head by an armored fiber cable. In this way, the power supply and diodes can be located remotely, while the laser head and harmonic conversion device are located in the semiconductor-processing machine. The power supply and diodes can be outside the machine or even outside the clean room.

However, positioning the diodes in the power supply, followed by coupling the diode pump light in a multimode fiber, works because the pump light is: in the IR, continuous wave, and not diffraction limited. In contrast, the output of the laser is visible or UV, is often pulsed, and has a diffraction limited beam. Thus, single mode fibers are required to preserve the beam quality, but are problematic with both pulses and UV radiation.

There is a need for improved UV and visible laser systems that are suitable for semiconductor inspection or processing. There is a further need for UV and visible laser systems for semiconductor inspection or processing applications where the laser resonator and power supply are positioned at a location external to a clean room.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide diode-pumped lasers, and their methods of use, in remote location applications.

Another object of the present invention is to provide diode-pumped lasers, and their methods of use, in semiconductor inspection or processing applications with the laser resonator and power supply positioned at a location external to a clean room.

These and other objects of the present invention are achieved in a laser apparatus that includes a modelocked laser system with a high reflector and an output coupler that define an oscillator cavity. An output beam is produced from the oscillator cavity. A gain medium and a modelocking device are positioned in the oscillator cavity. A diode pump source produces a pump beam that is incident on the gain medium. A second harmonic generator is coupled to the oscillator cavity. A third harmonic generator that produces a UV output beam, is coupled to the second harmonic generator. A photonic crystal fiber is provided with a proximal end coupled to the laser system. A delivery device is coupled to a distal portion of the photonic crystal fiber.

In another embodiment of the present invention, a laser apparatus includes a modelocked laser system with a high reflector and an output coupler that define an oscillator cavity and produces an output beam. A gain medium and a modelocking device are positioned in the oscillator cavity. A diode pump source produces a pump beam that is incident on the gain medium. A first amplifier is also included. A second harmonic generator is coupled to the first amplifier. A third harmonic generator that produces a UV output beam, is coupled to the second harmonic generator. A photonic crystal fiber is provided with a proximal end coupled to the laser system. A delivery device is coupled to a distal portion of the photonic crystal fiber.

In another embodiment of the present invention, a laser apparatus includes a modelocked IR laser system with a high reflector and an output coupler that define an oscillator cavity. A gain medium and a modelocking device are positioned in the oscillator cavity. A diode pump source produces a pump beam that is incident on the gain medium. A photonic crystal fiber is provided with a proximal end coupled to the IR laser system. A harmonic conversion delivery device is coupled to a distal end of the photonic crystal fiber.

In another embodiment of the present invention, a laser apparatus includes a modelocked IR laser system with a high reflector and an output coupler that define an oscillator cavity. A gain medium and a modelocking device are positioned in the oscillator cavity. A diode pump source produces a pump beam incident on the gain medium. A first amplifier is also included. A photonic crystal fiber has a proximal end coupled to the IR laser system. A harmonic conversion delivery device is coupled to a distal end of the photonic crystal fiber.

In another embodiment of the present invention, a method of delivering a UV output beam to a remote location provides a modelocked infrared laser system. The laser system includes a high reflector and an output coupler that define an oscillator cavity that produces an output beam. A gain medium and a modelocking device are positioned in the oscillator cavity. A photonic crystal fiber is provided and has a proximal portion coupled to the laser system, and a distal portion coupled to a delivery device. The infrared laser system is positioned at a distance from the remote location. A UV output beam is produced at a distance from the remote location. The UV output beam is delivered to the delivery device at the remote location.

In another embodiment of the present invention, a method of delivering an UV output beam to a remote location is provided. A modelocked IR laser system includes a high reflector and an output coupler that define an oscillator cavity that produces an output beam. A gain medium and a modelocking device are positioned in the oscillator cavity. A diode pump source produces a pump beam that is incident on the gain medium. A harmonic conversion delivery device is positioned at the remote location. A photonic crystal fiber is provided that has a proximal portion coupled to the IR laser system, and a distal portion coupled to the harmonic conversion delivery device. The IR laser beam is delivered with the photonic crystal fiber from the IR laser system to the harmonic conversion delivery device. A UV beam is produced from the harmonic conversion delivery device at the remote location.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1

is a block diagram that illustrates one embodiment of a laser or laser/amplifier system that produces UV light utilized with the systems and methods of the present invention.

FIG. 2

is a block diagram of one embodiment of a system of the present invention illustrating the combination of the system of

FIG. 1

, a photonic crystal fiber and a delivery device.

FIG. 3

is a block diagram that illustrates another embodiment of a laser or laser/amplifier system that produces IR light utilized with the systems and methods of the present invention.

FIG. 4

is a block diagram of one embodiment of a system of the present invention illustrating the combination of the system of

FIG. 3

, a photonic crystal fiber and a harmonic conversion delivery device.

FIG. 5

illustrates one embodiment of the present invention utilizing the systems of

FIG. 2

or

FIG. 4

in a remote location.

DETAILED DESCRIPTION

In various embodiments, the present invention provides a laser apparatus that has a laser system, and its methods of use. In one embodiment, the laser system includes an oscillator system or an oscillator/amplifier system. The oscillator/amplifier system is similar to the oscillator system but includes one or more amplifiers. The oscillator and oscillator/amplifier systems can be coupled with second, third, fourth, and fifth harmonic generators. A second harmonic generator can be used alone with the oscillator and oscillator/amplifier systems and in various combinations with third, fourth and fifth harmonic generators. Additionally, the harmonic generators can be coupled with an OPO. The OPO can be pumped by a fundamental beam from an oscillator or from the harmonic generators. An output of the OPO can be mixed with the harmonic generators to generate an additional variable wavelength source.

In one embodiment, the oscillator system includes an Nd:YVO

4

gain medium and is modelocked by a multiple quantum well absorber. In a specific embodiment of this oscillator system, the oscillator is pumped by a single fiber-coupled diode bar that provides 13 watts of pump power incident on the Nd:YVO

4

gain medium, and typically produces 5-6 watts of 5-15 picosecond pulses at 80 MHz repetition rate. In another embodiment, an oscillator/amplifier system includes an Nd:YVO

4

gain medium modelocked by a multiple quantum well absorber, a double pass amplifier and two single pass amplifiers. Each of the amplifiers has an Nd:YVO

4

gain medium and is pumped by two fiber-coupled diode pump sources. This oscillator/amplifier system produces 25-30 watts of 5-15 picosecond pulses at 80 MHz repetition rate. In another embodiment, a pumping wavelength of 880 nm is used for increased power with a similar value of the thermal lens in the gain medium.

The oscillator and oscillator/amplifier systems can be modelocked with a multiple quantum well saturable absorber, a non-linear mirror modelocking method, a polarization coupled modelocking method, or other modelocking techniques, including but not limited to use of an AO modulator. An example of a quantum well saturable absorber is disclosed in U.S. Pat. No. 5,627,854, incorporated herein by reference. An example of a non-linear mirror modelocking method is disclosed in U.S. Pat. No. 4,914,658, incorporated herein by reference. An example of a polarization coupled modelocking method is disclosed U.S. Pat. No. 6,021,140, incorporated herein by reference. In order to produce shorter pulses and a single output beam the gain media is positioned adjacent to a fold mirror as described in U.S. Pat. No. 5,812,308, incorporated herein by reference.

A high power oscillator system with the performance of an oscillator/amplifier system is achieved by using multiple fiber-coupled diodes and either a non-linear mirror modelocking technique or a polarization coupled modelocking method. This high power oscillator system produces 10-20 watts of output power with 4-10 picosecond pulses at a repetition rate of 80-120 MHz.

High repetition rates are desirable for applications where the laser system is used as a quasi-CW source. For some applications, 80 MHz repetition rate is sufficiency high to be considered quasi-CW. This repetition rate is achieved with an oscillator cavity length of 1.8 meters. When the cavity length is shortened to 0.4 meters the repetition rate increases to 350 MHz.

Referring now to

FIG. 1

, one embodiment of an oscillator system

10

has a resonator cavity

12

defined by a high reflector

14

and an output coupler

16

. A gain media

18

is positioned in resonator cavity

12

. Suitable gain media

18

include but are not limited to, Nd:YVO

4

, Nd:YAG, Nd:YLF, Nd:Glass, Ti:sapphire, Cr:YAG, Cr:Forsterite, Yb:YAG, Yb:glass, Yb:KGW, Yb:KYW, KYbW, YbAG, and the like. A preferred gain media

18

is Nd:YVO

4

. A modelocking device

19

is positioned in oscillator cavity

12

. In one embodiment, oscillator system

10

is modelocked and pumped by a fiber-coupled bar

20

that produces 13 watts of power. Oscillator cavity

12

can produce 1 to 6 watts of power nominally at an 80 MHz repetition rate with pulse widths of 5 to 15 picoseconds.

Optionally included are one or more amplifiers, generally denoted as

23

. An output beam

22

from resonator cavity

12

can be amplified by a first amplifier

24

. A second amplifier

26

can be included. Additional amplifiers may also be included to increase power. Typically, amplifiers

24

and

26

have the same gain media used in resonator cavity

12

. Nd:YVO

4

is a suitable gain media material because it provides high gain in an amplifier. The high gain of Nd:YVO

4

provides a simplified amplifier design requiring fewer passes through the gain media. Amplifiers

24

and

26

produce output beams

28

and

30

respectively. Amplifiers

24

and

26

can be single pass, double pass and four pass. A four pass amplifier is disclosed in U.S. Pat. No. 5,812,308, incorporated herein by reference. Oscillator/amplifier system

10

using an oscillator, a double pass amplifier and two single pass amplifiers can provide 30 watts of average power.

Output beams

22

,

28

or

30

can be incident on a harmonic generator generally denoted as

31

and can include a second harmonic generator

32

. An output

34

from second harmonic generator

32

can be incident on a third harmonic generator

36

to produce an output beam

40

. Alternatively, output

34

can be incident on a fourth harmonic generator

42

to produce an output beam

44

. It will be appreciated that oscillator system

10

can include various combinations of harmonic generators

32

,

36

,

42

as well as a fifth or higher harmonic generators or an OPO. Second harmonic generator

32

can use non-critically phase matched LBO, third harmonic generator

36

can employ type II LBO and fourth harmonic generator

42

can use type I BBO.

In a specific embodiment, oscillator system

10

includes oscillator cavity

12

with harmonic generation. Output beam

22

is incident on second harmonic generator

32

. In this specific embodiment, oscillator system

10

may also include third or fourth harmonic generators

36

and

42

. The output power of this oscillator system

10

is 5 watts at 1064 nm. A harmonic generation system produces 2 watts at 532 nm or 1 watt at 355 nm or 200 milliwatts at 266 nm.

In another specific embodiment, Nd:YVO

4

is the gain media of oscillator/amplifier system

10

, and 29 watts of 7 picosecond pulses at 1064 nm is produced. The harmonic generation system can generate 22 watts at 532 nm or 11 watts at 355 nm or 4.7 watts at 266 nm.

In another specific embodiment, oscillator/amplifier system

10

includes oscillator cavity

12

, a four-pass amplifier

24

and second harmonic generator

32

to produce 2 watts at 532 nm. This oscillator/amplifier system can pump an OPO that utilizes non-critically phase matched LBO as described in Kafka, et al., J. Opt. Soc. Am. B 12, 2147-2157 (1995) incorporated herein by reference.

In another specific embodiment, oscillator/amplifier system

10

includes oscillator cavity

12

, a double pass amplifier

24

and three single pass amplifiers

26

that produces 42 watts of 7 picosecond pulses at 1064 nm. This oscillator/amplifier system can pump an OPO using non-critically phase-matched KTA and produce an output beam at 1535 nm. The output beam at 1535 nm can be mixed with a 1064 nm beam to provide 11.6 watts at 629 nm, as described in Nebel, et al., in

Conference on Lasers and Electro

-

Optics,

Vol. 6 of 1998 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1998) postdeadline paper CPD3. Fiber-coupled bars that produce 40 Watts, commercially available from Spectra Physics Semiconductor Lasers, Tucson, Ariz. can be used to increase the output power of oscillator or oscillator/amplifier systems

10

.

The use of a Nd:YVO

4

gain media

18

with a doping level of less than 0.5% can also be used to increase the output power of oscillator or oscillator/amplifier systems

10

. The combination of the 40 watt fiber-coupled bars with the low doped Nd:YVO

4

gain media greatly increases the output power of oscillator and oscillator/amplifier systems

10

. Use of low doped Nd:YVO

4

gain media

18

can also reduce the sensitivity of oscillator cavity

12

to misaligmnent as well as improve the output beam quality from an amplifier

24

or

26

. The use of low doped Nd:YVO

4

gain media, a longer Nd:YVO

4

gain media as well as a larger pump volume in Nd:YVO

4

gain media is disclosed in U.S. Pat. No. 6,185,235, incorporated herein by reference. Oscillator system and/or oscillator/amplifier system

10

, are collectively designated as laser system

110

, and output beams

22

,

28

,

30

,

34

,

40

or

44

are collectively denoted as output beam

112

.

Referring now to

FIG. 2

, one embodiment of the present invention is a laser apparatus

100

that includes laser system

110

. A photonic crystal fiber

114

has a proximal portion

116

coupled to laser system

110

and a distal portion

118

coupled to a delivery device

120

. Suitable delivery devices include, but are not limited to, one or more lenses, mirrors, scanners, microscopes, telescopes, acousto-optic or electro-optic devices, and the like.

A characteristic of photonic crystal fiber

114

is that is has low absorption at the wavelength of interest. Additionally, the damage threshold and threshold for nonlinear effects are both high. By way of illustration, and without limitation, the threshold for nonlinear effects can be substantially greater than 1 kilowatt. In one embodiment, photonic crystal fiber

114

is a hollow core single mode photonic crystal fiber. Hollow core single mode photonic crystal fiber

114

guides output beam

112

in air and preserves its mode quality. These fibers are commercially available from Blaze Photonics, Bath, England.

As illustrated in

FIG. 3

, in another embodiment, laser system

210

is an IR laser system that produces an output of a wavelength between 1000 nm and 1100 and most preferably 1064 nm. The power range can be between 5 to 30 W.

IR laser system

210

is similar to laser system

10

but does not include the harmonic generators. IR laser system

210

has a resonator cavity

212

, high reflector

214

, output coupler

216

, a gain media

218

and a modelocking device

219

. IR laser system

210

is pumped by a pump source

220

and produces an output beam

222

. IR laser system

210

can include one or more amplifiers,

223

that amplify output beam

222

. Amplifier

223

can include a first amplifier

224

, a second amplifier

226

and additional amplifiers depending on the application.

Referring to

FIG. 4

, IR laser system

310

is similar to IR laser system

210

, and produces an output beam

312

. Output beam

312

is coupled to a photonic crystal fiber

314

, which in turn is coupled to a harmonic conversion delivery device

320

. Harmonic conversion delivery device

320

can include various combinations of harmonic generators

332

,

336

,

342

, as well as fifth or higher harmonic generators or an OPO, and a delivery device

338

which is substantially the same as delivery device

120

.

In one method of the present invention, laser systems

110

or

310

, collectively

410

, are positioned remotely from a remote location

422

. Delivery device

120

or harmonic conversion delivery device

320

, collectively

420

, is positioned at remote location

422

. Output beams

112

or

312

, collectively

412

, from laser

410

, is delivered by photonic crystal fiber

414

to delivery device

420

at a remote location

422

as shown in FIG.

5

. In the embodiment of IR laser

310

, its power supply, pump diodes, and IR laser head are all positioned away from remote location

422

. Examples of remote location

422

include clean rooms, vacuum enclosures, enclosed machinery and the like.

In one embodiment, remote location

422

is a clean room that is utilized in the semiconductor industry. However, it will be appreciated that the present invention also finds utility in a wide variety of different types of clean rooms, and other remote locations, where it is desired to position laser system

410

apart from remote location

422

.

In one embodiment, laser system

410

is positioned from 2 to 200 meters from remote location

422

. In another embodiment, laser system

410

is positioned no more than 10 meters from remote location

422

.

Laser system

410

is positioned away from remote location

422

and the heat produced by laser system

410

is not introduced to remote location

422

. By positioning laser system

410

away from remote location

422

, maintenance of laser system

410

can be carried out without disrupting remote location

422

as well as items located there.

The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the following claims and their equivalents.