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GB2037000A - Light guide - Google Patents

Light guide Download PDF

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Publication number
GB2037000A
GB2037000A GB7939559A GB7939559A GB2037000A GB 2037000 A GB2037000 A GB 2037000A GB 7939559 A GB7939559 A GB 7939559A GB 7939559 A GB7939559 A GB 7939559A GB 2037000 A GB2037000 A GB 2037000A
Authority
GB
United Kingdom
Prior art keywords
laser
pipe
laser beam
substrate
diffuser according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB7939559A
Other versions
GB2037000B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
SECR DEFENCE
UK Secretary of State for Defence
Original Assignee
SECR DEFENCE
UK Secretary of State for Defence
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by SECR DEFENCE, UK Secretary of State for Defence filed Critical SECR DEFENCE
Priority to GB7939559A priority Critical patent/GB2037000B/en
Publication of GB2037000A publication Critical patent/GB2037000A/en
Application granted granted Critical
Publication of GB2037000B publication Critical patent/GB2037000B/en
Expired legal-status Critical Current

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24Coupling light guides
    • G02B6/42Coupling light guides with opto-electronic elements
    • G02B6/4296Coupling light guides with opto-electronic elements coupling with sources of high radiant energy, e.g. high power lasers, high temperature light sources
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0643Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising mirrors
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24Coupling light guides
    • G02B6/26Optical coupling means
    • G02B6/262Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B2006/0098Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings for scanning
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12166Manufacturing methods
    • G02B2006/12169Annealing
    • G02B2006/12171Annealing using a laser beam

Landscapes

  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Lasers (AREA)

Abstract

A laser beam diffuser for use in laser beam annealing comprises a silica laser beam guiding pipe (3), having a diffusing surface (6) or layer at one end and a polished surface (12) at the other end. The diffusing surface (6) may be a ground surface. A bend (8) or bends removes axial component of speckle produced by the ground surface. Adjacent the polished end (12) the pipe may be of reduced cross section (10, 11). <IMAGE>

Description

SPECIFICATION Laser beam annealing This invention concerns the annealing of semiconductor material by beams of laser radiation, in particular it provides a diffuser for a laser beam.
Laser beam annealing is described in.Science, Vol. 201, 28 July, 1978, pages 333-335.
One use of !aser beam annealing is the annealing of ion-implanted semiconductor layers to electrically activate the implanted dopant.
Typically the dopant is implanted to 3 depth of 0.05-0.4 ym. Substrates may be annealed by heating in an oven but this may take an hour or so for each sample batch. In contrast laser annealing is quick and can be selective, i.e. portions of a substrate can be annealed leaving unannealed portions and the substrate is heated to a depth of typically less than 10 ,um. Laser radiation in the form of short e.g. 30 ns pulses can heat the surface sufficiently quickly to melt only approximately the top Mm. Unfortunately the energy applied to the substrate must be far more uniform than that present in a laser beam. It has been found that the energy intensity varies considerably across a beam of laser radiation i.e.
the mode pattern. This results in parts of a substrate receiving energy greatly in excess of that required with consequential erosion of the substrate, whilst other parts receive only the required energy density to anneal correctly.
Attempts to overcome this have used a diffusing ground glass screen between laser and substrate.
Unfortunately due to the wide angle dispersion introduced by the screen the available power density distribution at the substrate is of rounded Gaussian forms with insufficient amplitude at the edges of the beam. Also the screen may induce speckle which gives rise to locally intense radiation on the substrate and consequential pitting of the surface.
According to this invention a laser beam diffuser for use in laser beam annealing comprises a laser beam guiding pipe having at one end a diffusing surface and at its other end a polished surface.
The diffusing surface may be a ground surface in which case the pipe is provided with a bend, typically a 900 bend, to remove especially the axial component of the speckle produced by the ground surface. The bend may be a simple bend in a single plane or a bend or bends in more than one plane, eg. a part of a spiral. The bend or bends should be -sufficient to prevent a direct, straight line, passage of light between the two ends of the pipe. Alternatively a diffusing layer, e.g. of opal, may be fixed to the end of the pipe.
Adjacent the polished end the pipe may be tapered to concentrate the laser beam power and to increase the laser beam divergence so improving the homogenization process.
The pipe may be silica of a high optical transparency at the laser wavelength or another glass with suitable tranmission properties. The guide should have a smooth curved surface to internally reflect the laser light during its passage from the diffusing to the polished end.
Apparatus for laser beam annealing comprises a laser whose output is directed onto the diffusing end of the light pipe, and a table for mounting a substrate close to the polished end of the pipe. The laser may be used in either pulse#d or CW modes.
The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows apparatus for laser beam annealing, and Figure 2 shows to an enlarged scale the diffuser in Figure 1.
As shown a Q switched Nd-YAG or Ruby laster 1 is arranged to direct its output beam 2 into a silica light pipe 3. A substrate 4 to be annealed is placed close to the pipe 3 on a movable table 5.
The laser used depends on the absorption of the substrate relative to the laser wavelength. A typical Nd-YAG or Ruby laser gives an output radiation energy density in the range 0.1 - 1 Joule/cm2.
The end of the pipe 3 nearest the laser 1 , the input end 6, is ground flat with diamond compound (typically 6 or 1 4cm). From the diffusing end 6 the pipe of 1 cm diameter extends straight for about 10 cm and is then bent into a 900 bend 8 of about 4 cm radus. Very small (~1 cm) radii of curvature give unacceptable loss of light through the side-wall. The purpose of the bend 8 is to give random multiple reflections from the walls to remove especially axial speckle generated by the ground end surface 6. Beyond the bend 8 the pipe extends at 9 for about 6 cm and is then tapered 10 smoothly over a length of about 1 cm to reduce the pipe diameter to about 0.65 cm.This reduced diameter 1 1 continues for about 6 cm and terminates in an optically polished end 12, which may have a flat or slightly curved face.
The tapered section 9 increases the power density to compensate for losses in the pipe, typically 37%. Final laser spot intensity variations can be less than -5%.
The reduced diameter portion 10 must be short enough to avoid build up of intensity on the pipe axis but not too short, otherwise reflections from the tapered section 9 can cause focussing and final homogenisation will be incomplete.
Alternatively, additional guide curvature may be introduced to suppress residual radiation inhomogeneities.
It is necessary to position the substrate 4 close e.g. T mm to the pipe output end 11 to give a uniform intensity of laser beam onto the substrate. Alternatively the output spot can be projected onto the substrate by use of a suitable lens system.
In use a substrate is doped by conventional ion implantation techniques and placed on the table 5.
Such implantation produces a highly damaged or amorphous surface layer due to the atom displacements caused by the penetration of ions into the crystal lattice. The laser 1 is repetitively fired and the substrate moved between successive bursts of the laser beam. By this means selected areas of the substrate are annealed to remove damage caused by the ion implantation and restore the substrate to a crystalline state and e.g.
provide electrically conducting path amongst an insulating non-annealed substrate.
Alternatively the laser may be fired repetitively onto one spot on the substrate to effect a segregation of dopant to the surface as the substrate cools between each firing.
Examples of materials that can be laser annealed are ion implanted silicon germanium or diamond where the ions are implanted by conventional techniques to a typical depth of about 0.2 #m. The dopant ions may be phosphorus, boron arsenic, aluminium, gallium, indium, copper, iron, nickel, gold and platinum.
the laser power received on the substrate for single shot annealing is about 0.5 to 3 Joule/cm2 for about 30 nano secs to anneal to a depth of about less than 1 mum. For repetitive laser firing onto a spot the laser power may be reduced below 0.5 Joule/cm2. This may not melt the amorphous layer but heat it sufficiently to cause recrystallisation after repeated heating.
Resolidification of a melted substrate surface takes place in about 1 us.
Other materials suitable for laser annealing include indium phosphide, gallium arsenide and indium\arsenide doped with ions of sulphur, selenium tellurium, zinc, cadmium, silicon, germanium, tin or argon; the compound alloy cadmium mercury telluride doped with e.g.
aluminium, mercury, or protons of hydrogen bombardment. For single shot annealing of InP typical laser power on the substrate is between 0.1 to 1 Joule/cm2 and less for multi shot operation.
Some Ill-V compounds cannot be conventionally annealed because some constituents preferentially evaporate off on heating. However the short period of heating provided by the laser beam enables annealing to be performed with reduced loss of volatile component.
For example InP when heated in an oven preferentially evaporates phosphorus to leave an indium rich surface. Laser beam annealing for small number of laser bursts, does not allow significant amounts of phosphorus to evaporate.
Repeated applications of the laser may result in appreciable evaporation of phosphorus. In these cases the substrate may be coated with a layer of silicon nitride to prevent phosphorus evaporation.
Also some dopants e.g. nickel cannot be conventionally annealed because the dopant diffuses too widely. Laser annealing allows annealing with minimal diffusion.
Laser annealing may also be applied to the surface annealing of metals e.g. to relieve surface stress in ferrous or non ferrous metals and alloys of such metals.
The light pipe 3 may be any other suitable size, circular or other cross section, and with or without a reduced diameter end. The relevant sizes are determined by the laser beam 2 diameter and power available, and size of annealing spot required. For example two other pipes had the following dimensions:~ (i) pipe diameter at 7, 0.5 cm, length 7, 7 cm, length 9, 3 cm, taper length 10, 2 cm, length 11, 3 cm, diameter at 12,0.17cm; (ii) pipe diameter at 7, 0.5 cm, length 7, 5 cm, length 9, 2 cm, taper length 10, 1 cm, length 22, 4 cm, diameter at 12, 0.12 cm.
The polished end 12 may be coated with an anti-reflection coating e.g. MgF. Also the pipe 3 may be coated in part or whole to provide maximum internal reflection of the laser light When the diffuser end 6 of the pipe is a ground surface the speckle produced can be removed by a bend 7 which for some cases is about 90 ; increasing the amount of bend does not improve the homogeneity of the laser beam and only absorbs laser power. Reducing the bend below 900 is possible but values much lower than 900 can allow speckle to pass through the pipe 3 and damage the substrate. However, adding a second curve can once again reduce speckle intensity.
To overcome speckle a layer of e.g. opal may be fixed on the end 6 to provide a speckle free diffuser. In this case the end 6 is not ground and the bend 7 may not be required.

Claims (10)

1. A laser beåm diffuser for use in laser beam annealing characterised by a laser beam guiding pipe (3) having at one end a diffusing surface (6) and at the other end a polished surface (12).
2. A diffuser according to claim 1 characterised in that the diffusing surface (6) is a ground surface.
3. A diffuser according to claim 2 characterised by a bend (8) between the two ends (6, 12).
4. A diffuser according to claim 3 characterised by bends (8) in more than one plane.
5. A diffuser according to claim 1 characterised by a tapered portion (10) leading to a reduced cross section portion (1 1).
6. A diffuser according to claim 1 characterised by a pipe (3) of silica having a high optical transparency at a laser wavelength.
7. A diffuser according to claim 1 characterised in that the diffusing surface (6) is a layer of diffusing material.
8. A diffuser according to claim 7 characterised by a diffusing layer of opal material.
9. A diffuser according to claim 1 characterised by antireflection coating on the polished end 12.
10. A diffuser according to claim 1 characterised by antireflection coating on the surface between the two ends (6, 12).
GB7939559A 1978-11-24 1979-11-15 Light guide Expired GB2037000B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB7939559A GB2037000B (en) 1978-11-24 1979-11-15 Light guide

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB7846015 1978-11-24
GB7939559A GB2037000B (en) 1978-11-24 1979-11-15 Light guide

Publications (2)

Publication Number Publication Date
GB2037000A true GB2037000A (en) 1980-07-02
GB2037000B GB2037000B (en) 1982-11-03

Family

ID=26269731

Family Applications (1)

Application Number Title Priority Date Filing Date
GB7939559A Expired GB2037000B (en) 1978-11-24 1979-11-15 Light guide

Country Status (1)

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GB (1) GB2037000B (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0048514A1 (en) * 1980-09-18 1982-03-31 L'Etat belge, représenté par le Secrétaire Général des Services de la Programmation de la Politique Scientifique Process for crystallising films, and films thus obtained
GB2154017A (en) * 1984-02-03 1985-08-29 Gen Electric Laser material processing through a fiber optic
GB2180363A (en) * 1985-09-13 1987-03-25 Stc Plc UV laser beam homogeniser comprising bent tubular waveguide
FR2651508A1 (en) * 1989-09-05 1991-03-08 Centre Nat Rech Scient DEVICE FOR PROCESSING LASER SHOCK PARTS.
WO2002084237A1 (en) * 2001-04-11 2002-10-24 Rio Grande Medical Technologies, Inc. Illumination device and method for spectroscopic analysis
DE102010020156B4 (en) * 2009-05-15 2025-12-31 Günther Nath Lighting device with radiation homogenization

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0048514A1 (en) * 1980-09-18 1982-03-31 L'Etat belge, représenté par le Secrétaire Général des Services de la Programmation de la Politique Scientifique Process for crystallising films, and films thus obtained
GB2154017A (en) * 1984-02-03 1985-08-29 Gen Electric Laser material processing through a fiber optic
GB2180363A (en) * 1985-09-13 1987-03-25 Stc Plc UV laser beam homogeniser comprising bent tubular waveguide
GB2180363B (en) * 1985-09-13 1989-09-06 Stc Plc Beam homogeniser
FR2651508A1 (en) * 1989-09-05 1991-03-08 Centre Nat Rech Scient DEVICE FOR PROCESSING LASER SHOCK PARTS.
EP0416988A1 (en) * 1989-09-05 1991-03-13 Centre National De La Recherche Scientifique (Cnrs) Device for laser shock treatment of work pieces
WO2002084237A1 (en) * 2001-04-11 2002-10-24 Rio Grande Medical Technologies, Inc. Illumination device and method for spectroscopic analysis
US6862091B2 (en) 2001-04-11 2005-03-01 Inlight Solutions, Inc. Illumination device and method for spectroscopic analysis
DE102010020156B4 (en) * 2009-05-15 2025-12-31 Günther Nath Lighting device with radiation homogenization

Also Published As

Publication number Publication date
GB2037000B (en) 1982-11-03

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Legal Events

Date Code Title Description
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee