EXCIMER LASER MICROMACHINING FUNDAMENTALS

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EXCIMER LASER MICROMACHINING FUNDAMENTALS
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(No Transcript)
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PROPERTIES OF EXCIMER LASERS

• EMISSION WAVELENGTH DETERMINED BY THE GAS
  MIXTURE USED AND THE EXCITED DIMER PRODUCED IN
  THE LASER DISCHARGE. EMISSION WAVELENGTH
  EXCITED DIMER 157 nm
  F2 ? 193 nm ArF ? 248
  nm KrF 308 nm XeCl
  351 nm XeF (? MIT/CBA
  SYSTEM)

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248 nm EXCIMER DISCHARGE
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Electrical Discharge
e
e
Collision with Neon Atom
Population Inversion
UV Photon
Relaxation Time 100ms
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EXCIMER BEAM PROFILE
24 mm
8 mm
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CONVENTIONAL FOCAL POINT MACHINING WITH CO2 AND
NDYAG LASERS
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EXCIMER MASK PROJECTION IMAGING(NEAR FIELD
IMAGING)
I
O
f
Projected Image
Imaging Lens
Mask
O object distance (distance from mask plane to
lens plane) I image distance (distance from
lens plane to target plane) f focal length of
the imaging lens
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BASIC OPERATIONAL RELATIONSHIPS

• D demagnification ratio (reduction factor from
  mask to target)
• O object distance (distance from mask plane to
  lens plane)
• I image distance (distance from lens plane to
  target plane)
• FT energy density (fluence) on target (J/cm2)
• FL energy density (fluence) at the mask plane
  (raw beam) (J/cm2)
• f focal length of the imaging lens
• eff efficiency (throughput) of the beam
  delivery system
• D O / I FT FL x D2 x eff 1 / f 1
  / I 1 / O

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PROJECTION MASK OPTIONS

• Motorized Variable Rectangular Aperture-
  Independent X and Y control, symmetric opening
  and closing- Aperture size continuously
  adjustable from 15 mm to lt 0.1 mm.
• Chemically Etched Metal Masks- Fixed apertures
  of any geometry that can be created as a
  stencil.- SS foils typically from 50 µm (0.002)
  to 250 µm (0.010) thick. - Minimum line widths
  to 175 µm (0.007).
• Aluminum-on-Quartz Masks- Similar to
  Cr-on-Quartz mask technology used for
  lithography. - Excimer grade fused silica
  substrates.- Line widths to lt 10 µm, for high
  resolution or special geometries.

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EXCIMER ABLATION PROCESS
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MATERIAL INTERACTION WITH UV PHOTONS

• Photochemical Color Change- Occurs in some
  plastics and ceramics at low energy densities.-
  UV photons alter surface molecular structure
  resulting in a change of light absorbing
  properties (color).
• Photochemical Ablation- At higher energy
  densities (above ablation threshold),
  absorption of UV photons results in breaking of
  molecular bonds in material.- The small
  interaction volume due to a shallow absorption
  depth (0.1 0.3 µm) limits heat conduction (for
  material with a high absorption cross-section at
  the process wavelength).- Ablation by-products
  and excess energy are carried away by the
  ablation plasma.

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• Thermal Effects
• - As energy density increases, the absorption
  depth increases resulting in a larger interaction
  volume and increased heat conduction to the
  surrounding material.- Even at low energy
  densities, radiative coupling of energy from the
  ablation plasma may induce thermal effects,
  depending on the sensitivity of the material.-
  As the laser pulse repetition rate increases,
  boundary layer thermal gradients increase as
  influenced by thermal properties of the
  material.- Absorption of UV photons below
  ablation threshold will result in heating of the
  material.- Certain materials such as metals are
  removed by a purely thermal melting and
  vaporizaton process.

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10 µm DIA. HOLE IN 50 µm THICK Pt/Ir ALLOY FOIL
entrance surface
exit surface
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100 µm SQUARE HOLE ARRAY IN 2 µm THICK Zn FOIL
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30 µm DIA. HOLE ARRAY IN 25 µm THICK MYLAR FILM
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EXCIMER STRIPPING OF POLYIMIDE COATED FUSED
SILICA CAPILLARIES
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TEST DRILLING OF ICF TARGET SPHERES165 µm WALL
THICKNESS POLYIMIDE
25 µm entrance holes
5 µm exit holes (oblique view showing hole taper)
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ION TRAP STRUCTURE IN 250 µm THICK ALUMINA
200 µm /100 µm stepped main channel with 45
knife edge side walls and 20 µm side slits
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3-D SINUSOIDAL STRUCTURE ON POLYIMIDE
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GRID PATTERN IN THIN FILM GOLD METALLIZATION ON
CERAMIC
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10 µm SQUARE POST GRID IN ZIRCONIA
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FLAT BOTTOMED CHANNEL INTERSECTION IN POLYIMIDE
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HOLE DRILLING IN 1 mm THICK ALUMINA
entrance surface 260 µm dia.
exit surface 200 µm dia.
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3-D PILLAR STRUCTURE IN POLYCARBONATE
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HOLES AND SLOTS IN 1.7 mm DIA. CATHETER EXTRUSION
400, 250, and 75 µm dia. holes
0.4 mm W x 2.2 mm L slot
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RapidX 250 Micromachining System Presentation

• System Configuration
• RPC Software Menus
• RPC Programming Language
• DXF Preprocessor

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RapidX250 System Configuration
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RapidX250 Workstation
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RapidX250 Layout
M3 Turning Mirror
M2 Turning Mirror
Motorized RVA
Camera Lenses
Attenuator
Stage Stack
Mask Holder
Computer and Motion Driver
M1 Turning Mirror
Entrance Window
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Focusing Lens, Camera Viewing
Aperture Stop
Camera
Projection lens
Camera Focus
Focus Adjust
Debris Nozzle
Camera Lens
Work Piece
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Projection Lens vs Energy on Target
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Mask holder
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Mask Set
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Motorized Rectangular Variable Aperture (RVA)
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Beam Attenuator
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Stage Stack
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Facility Requirements
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Pneumatics
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RPC Software

• Operator Menu
• Engineering JOG Menu
• File Menu

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Operator Menu
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Engineering JOG Menu
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Home Axis
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Zero Axis Position
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Preset Axis Positions
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Program Menu
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Select a Program File (.OMS)
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Run Process File
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RPC Programming Language

• Motion laser firing Commands
• Logical program flow control
• Strings, Variables and math. Functions
• User input/output
• Internal and external subroutine calls

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Motion Axis

• X X Left/Right stage
• Y Y Front/Back stage
• Z Z Lift stage
• T Laser pulses
• U Goniometer stage
• V Rotary stage
• R Aperture X
• S Aperture Y

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Axis Commands

• Select Axis - AX
• AX Selects X axis
• AY Selects Y axis
• AZ Selects Z axis
• AT Selects T axis
• AU Selects U axis
• AV Selects V axis
• AR Selects R axis
• AS Selects S axis
• AA Selects all axis
• Set Velocity - VL
• AA VL1,1,,150 Set XY velocities to 1mm/s,
  set T laser to 150 Hz
• Set Acceleration - AC
• AA AC15,15 Set XY accelerations to 15 mm/s
• Load Position - LP
• AA LP0,0 Sets current stage position to
  x0 and y0

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Axis Commands, Contd

• Point-to-Point independent absolute move - MA
• AA MA1,3 Move to position x1mm, y2mm
• Point-to-Point independent relative move -
  MR
• AA MR-5,0 Move X relative -5mm from current
  position
• AT MR200 Fire 200 pulses on T laser axis
• Point-to-Point interpolated absolute move -
  ML
• AA ML1,3 Move to position x1mm, y3mm with
  interpolation
• Point-to-Point interpolated relative move -
  MT
• AA MT1,3,,150 Move to position x1mm, y3mm
  and fire 150 .
  pulses with interpolation

B
B
Y
Y
Independent Move
Interpolated Move
A
A
X
X
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Laser Cutting Drilling

• 1. Percussion Drilling
• Laser repetition rate
• Number of pulse
• AA VL10 MA20,25 Move to
  position x20, y25 at 10mm/s
• WT5 Settle for 5 ms
• AT VL200 MR750 Fire 750
  pulses at 200 Hz
• 2. Scanning / Cutting
• Scan velocity
• Pulse spacing

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Laser Cutting Contd

• Example - Linear Cut
• AA VL1,1,,100 Set XY velocities at 1mm/s,
  set laser pulse rate 100Hz
• LP0,0 Set current stage
  position as origin (0,0)
• MA5,7 Move to initial point
  (5,10)
• CUTREL 4,0 Cut bottom side (Same as
  MR4,0,0,400)
• CUTREL 0,2 Cut right side (Same
  as MR0,2,0,200)
• CUTREL -4,0 Cut top side (Same
  as MR-4,0,0,400)
• CUTREL 0,-2 Cut left side (Same
  as MR0,-2,0,200)

2mm
(5,7)
4mm
(0,0)
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Laser Cutting Contd

• Example - Circle and Arc Cut
• AA VL1,1,,100 Set XY velocities at 1mm/s,
  set laser pulse rate 100Hz
• LP0,0 Set current stage
  position as origin (0,0)
• MA6,2 Move to initial point
  (5,10)
• CIRCLE 5,2,1,0,90,1 Cut circle, Center
  (5,2), Radius1mm,
• Start
  angle00., Final angle900
• MA2.5,8 Move to beginning
  of circle
• CIRCLE 2,3,0.5,0,360,1 Cut circle, Center
  (2,3), Radius 0.5mm,
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  Start angle00., Final angle3600

P3(5,3)
P5 (2.5,3)
P4 (2,3)
P1 (5,2)
P2 (6,2)
P0 (0,0)
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Resonetics DXF Preprocessor
CAD Drawing
Motion Code (CAM)

• Open DXF file
• Select cutting layers
• Identify Sort cutting features
• Set direction and entry point
• Set starting point
• Set laser and cutting parameters
• Generate CNC code

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Resonetics DXF Preprocessor.
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Open file menu, select DXF file.
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Select what layer to cut.
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Select drawing system of unit.
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Drawing is displayed.
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System of Coordinates.
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Select new origin stating point.
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Virtual Simulation of cutting path.
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Reverse cutting contour direction
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Change Piecing Point.
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Change contour order.
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Set Preferences (output unit).
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Set Laser beam size.
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Set Cutting parameters.
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Generate OMS code.