1. Laser Dicing (Wafer Cutting) by Laser-Microjet®
SYNOVA
Innovative Laser Systems

2. Wafer Dicing
Semiconductor Wafers are cut into individual chips (dies), a processing step in the so-called back-end semiconductor production.
Cutting kerf
Die
Semiconductor Wafer
Street
March 2003
Laser Microjet Dicing

3. Today’s Technique: Sawing
Sawing with abrasive diamond blades
Diamond particles
High-speed rotary blade
Semiconductor Wafer
March 2003
Laser Microjet Dicing

4. Problems with Sawing Chipping High residual stress (micro-cracks)
Low speed
Only straight cutting possible
Un-adapted to thin wafers
De-lamination
Continuous wearing out of the blade
High running costs
Chipping
Street
The possibilities of abrasive cutting have reached their limits.
March 2003
Laser Microjet Dicing

5. Conventional Laser for Wafer Dicing?
Laser beam
Laser light is characterised as light waves of equal frequency and phase, which can be bundled at high intensity on account of their negligible divergence.
Focusing lens
Cutting gas
The focused laser beam heats material to temperatures of several thousand degrees, causing it to melt and/or evaporate.
Focus
Workpiece
An additional gas-jet expels the molten material from the cut.
March 2003
Laser Microjet Dicing

6. The Failure of the Conventional Laser
Profound thermal effects upon silicon
give rise to cracks and structural changes, such as burrs
and deposits on the wafer surface.
Thermal damages
Contamination
Example of a conventional laser cut
March 2003
Laser Microjet Dicing

7. New Lasers for Wafer Dicing?
Lasers with short wavelength
(UV lasers) and short pulse
(switched lasers) reduce heat damage and contamination
Problems:
Although reduced, contamination and heat damage persist
Low speed due to low laser power
Short pulse UV lasers allow
thermal damage and contamination
reductions, inherent in laser cutting,
but at the expense of reduced productivity.
March 2003
Laser Microjet Dicing

8. The Solution: Laser Microjet® (LMJ) Dicing
The Laser Microjet ® dicing technology applies a water jet guided laser, allowing high speed and high quality.
The problems of heating and contamination are solved by the simultaneous use of the water jet which conducts heat away from the material before the heat can damage it.
Example of a water jet guided laser cut
March 2003
Laser Microjet Dicing

9. The Advantages of Laser Microjet Dicing
No chipping
No mechanical damage (cracks), high fracture strength
Ideal for thin wafers
Omnidirectional cutting (any shape can be cut)
High speed
No tool wear, low running costs
March 2003
Laser Microjet Dicing

10. No Chipping
The force generated by the water jet is very low, because the diameter of the water jet is very small. As a result, the mechanical force is negligible.
Ablation is by absorption of laser light and heating.
The result is a force free, non-mechanical cutting, which avoids completely the chipping of the edges.
Sawing
Laser Microjet ® Dicing
March 2003
Laser Microjet Dicing

11. High Fracture Strength
The absence of heat penetration into the material prevents micro-cracks and generates a high fracture strength
A european chip manufacturer compared the fracture strength of 100 micron thick silicon wafers diced with LMJ technology against those with abrasive blade sawing
Force
Force
Silicon Chip
Fracture Strength
Average Force
Beam Bending Test
Ball Bending Test
3.68 N
Saw
27.46 N
5.83 N
LMJ
41.48 N
The LMJ diced chips have significantly higher fracture strength than sawed chips.
March 2003
Laser Microjet Dicing

12. Example: 100 micron thick memory chip diced by LMJ
Ideal for Thin Wafers
Wafers are thinned for stacked chips,
smart cards, and smart labels in order to save volume or to reach mechanical flexibility.
Thin wafers are presently between 50 and 150 microns thick. In the future, thicknesses of 25 microns and less will be used.
Example: 100 micron thick memory chip diced by LMJ
March 2003
Laser Microjet Dicing

13. Omnidirectional Cutting
The LMJ dicing allows for cutting
in any direction due to its point-like tool.
Slots
Holes
Contours
T-cuts
March 2003
Laser Microjet Dicing

14. High Speed
In the case of thin wafers, the LMJ dicing is faster than the saw
LMJ
Cutting
speed
[mm/s]
Throughput of 50 m wafers
15 wafers/hour
3 wafers/hour
Sawing speed
Saw
LMJ
Wafer thickness [micron]
The typical speed of a saw is 60 mm/s,
but the real cutting speed is only 40 mm/s as the saw makes a return without cutting, contrary to the LMJ which can cut in any direction.
The thinner the wafer is, the greater the advantage is in the throughput.
March 2003
Laser Microjet Dicing

15. Low Running Costs
The LMJ technology has significantly lower, running, hourly costs than sawing.
In the case of thin wafers, the high throughput allows substantial cost savings.
8.38 €/h
Investment
16.00 €/h
Cost of Ownership
6.80 €/h
Consumption DI water
0.23 €/h
Saw
LMJ
8.33 €/h
Consumption Blades
0 €/h
0 €/h
Consumption Lamps
1.20 €/h
0 €/h
Consumption Glasses, Nozzles
0.64 €/h
0.20 €/h
Consumption Electricity
0.90 €/h
The Complete Cost of Ownership Comparison,
made with a european chip manufacturer, is available.
1.56 €/h
Consumption Gas
0.66 €/h
1.23 €/h
Cleanroom Costs
1.32 €/h
11.39 €/h
Operator costs
6.83 €/h
37.89 €/h
Total running costs
27.79 €/h
Need of equipment for 50 m wafers
5 machines
1 machine
Cost saving per year with LMJ -1.3 million €
Cost saving after 5 years -6.5 million €
March 2003
Laser Microjet Dicing

16. The LaserTape® For the Laser Microjet Dicing an optimal tape
has been developed.
The so-named LaserTape® is ideal
for the LMJ dicing. Uneffected by the laser,
the basic film is transparent and porous, allowing the water jet to pass through without tearing.
The LaserTape® has a UV-curable adhesive, making it ideal for thin wafer dicing,
due to the adhesive strength reduction after UV curing.
The LaserTape® can be utilised in taping machines, and in pick-and-place machines.
The LaserTape® is available in two different back films and in various adhesive strengths.
The LaserTape® is manufactured and distributed by Furukawa (Japan)
March 2003
Laser Microjet Dicing

17. New Technology Opens New Possibilities
In the future, chip designers will have entirely new possibilities benefitting from unlimited chip shapes.
Round chips, hexagonal chips, different chip sizes on one wafer, any geometry is possible.
Chips of the future will be adapted to the requirements of emplacement.
Example of wafer cut into round chips
March 2003
Laser Microjet Dicing

18. The Future of Laser Microjet Dicing
Reduction of kerf width
25 microns and less
Increasing of cutting speed
of up to 1000mm/s
25 mm
1000 mm/s
March 2003
Laser Microjet Dicing

19. The Laser Dicing System
March 2003
Laser Microjet Dicing

20. Laser Dicing Video
March 2003
Laser Microjet Dicing