Advances in Laser Micro-machining for Wafer Probing and Trimming
Advances in Laser Micro-machining for Wafer Probing and Trimming
Advances in Laser Micro-machining for Wafer Probing and Trimming
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<strong>Advances</strong> <strong>in</strong> <strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g <strong>for</strong><br />
<strong>Wafer</strong> Prob<strong>in</strong>g <strong>and</strong> Trimm<strong>in</strong>g<br />
M.R.H. Knowles, A.I.Bell, G. Rutter<strong>for</strong>d & A. Webb<br />
Ox<strong>for</strong>d <strong>Laser</strong>s<br />
June 10, 2002<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 1
■<br />
■<br />
■<br />
■<br />
Introduction to <strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g<br />
<strong>Laser</strong> micro-hole drill<strong>in</strong>g <strong>for</strong> probe cards<br />
<strong>Laser</strong> trimm<strong>in</strong>g of MEMS<br />
Conclusions<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 2
Introduction to <strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 3
<strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g - Ablation<br />
<strong>Laser</strong> Ablation - material removal by a<br />
comb<strong>in</strong>ation of evaporation <strong>and</strong> melt expulsion<br />
Proportion of evaporation vs melt expulsion<br />
depends on laser parameters <strong>and</strong> material<br />
<strong>Laser</strong> Beam<br />
Ejected material<br />
Deposited Ejected Material<br />
Recast material<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 4
<strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g - Ablation<br />
General Rule (with notable exceptions)<br />
• Shorter wavelength removes less material<br />
• Shorter pulse removes less material<br />
• Less Material removed = higher precision<br />
• Less material removed - benefits from higher pulse rate<br />
Volume of Material Removed<br />
Wavelength<br />
Pulse Duration<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 5
<strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g<br />
Importance of correct choice of laser & process<br />
Holes <strong>in</strong> 1mm thick Steel<br />
Optimum <strong>Laser</strong> Parameters<br />
Clean hole with no recast<br />
almost no debris<br />
Non-Optimum <strong>Laser</strong> Parameters<br />
Significant recast, crown <strong>and</strong><br />
debris<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 6
CVL & UV CVL Characteristics<br />
Copper Vapour <strong>Laser</strong><br />
<strong>Laser</strong> type used <strong>in</strong> this presentation<br />
<strong>Laser</strong> CVL UV-CVL<br />
Wavelength (nm) 511& 578 255, 271 or 289<br />
Power (W) 10 - 50 1<br />
Pulse Freq (kHz) 1 - 50 4 - 10<br />
Pulse duration (ns) 10 - 50 10 - 50<br />
Beam quality (xDL) 1 - 2 1 - 2<br />
Integrate CVLs <strong>and</strong> solid state lasers <strong>in</strong>to turnkey<br />
systems depend<strong>in</strong>g upon the application<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 7
<strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g - Cutt<strong>in</strong>g<br />
Fixed Beam<br />
XY L<strong>in</strong>ear Axes<br />
Very High Accuracy<br />
Large Area<br />
Moderate velocity & acceleration<br />
Mov<strong>in</strong>g Beam<br />
XY Galvo Mirrors & Flat-field lens<br />
Moderate Accuracy<br />
Moderate Area<br />
Very high velocity & acceleration<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 8
<strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g - Drill<strong>in</strong>g<br />
Percussion<br />
Mask Imag<strong>in</strong>g<br />
Fixed Beam<br />
Hole size & Shape determ<strong>in</strong>ed by beam<br />
Low Accuracy & Quality<br />
High speed<br />
Fixed Beam<br />
Hole size & Shape determ<strong>in</strong>ed by Mask<br />
High Accuracy & Quality<br />
Moderate speed<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 9
<strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g - Drill<strong>in</strong>g<br />
Dedicated<br />
Trepann<strong>in</strong>g<br />
Device<br />
XY Galvo<br />
Mirrors<br />
Mov<strong>in</strong>g Beam<br />
Circular holes only<br />
Very High Accuracy & Quality<br />
Moderate speed<br />
Mov<strong>in</strong>g Beam<br />
Any hole shape<br />
High Accuracy<br />
Moderate Speed<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 10
CVL <strong>Micro</strong>-hole Drill<strong>in</strong>g<br />
Ø 100 µm <strong>in</strong><br />
1mm steel<br />
Holes from 1 µm diameter upwards<br />
Ø 50 µm <strong>in</strong> 0.1mm<br />
sta<strong>in</strong>less steel<br />
Ø 5 µm <strong>in</strong> 0.05 mm<br />
sta<strong>in</strong>less steel<br />
Ø 1 µm <strong>in</strong><br />
0.05 mm gold<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 11
<strong>Micro</strong>-hole Drill<strong>in</strong>g<br />
Through-holes<br />
Bl<strong>in</strong>d-holes<br />
Polyimide<br />
Polyimide<br />
Polyimide<br />
Kapton on copper<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 12
<strong>Micro</strong>-hole Drill<strong>in</strong>g/<strong>Micro</strong>-Cutt<strong>in</strong>g<br />
Silicon<br />
Diamond<br />
Polyimide<br />
Steel<br />
Ceramic<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 13
<strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g<br />
<strong>Micro</strong>-Mill<strong>in</strong>g<br />
Etch<strong>in</strong>g<br />
Copper<br />
Copper on Kapton<br />
PZT<br />
Alum<strong>in</strong>ium on Polymer<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 14
<strong>Laser</strong> <strong>Micro</strong>-mach<strong>in</strong><strong>in</strong>g - Materials<br />
Alum<strong>in</strong>a Silicon Nitride Steel<br />
Diamond<br />
Silicon<br />
Silicon<br />
Sapphire<br />
Metal on ceramic<br />
Polyimide<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 15
<strong>Laser</strong> <strong>Micro</strong>-hole Drill<strong>in</strong>g <strong>for</strong> Probe Cards<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 16
<strong>Laser</strong> <strong>Micro</strong>-hole Drill<strong>in</strong>g <strong>for</strong> Probe Cards<br />
Vertical<br />
probe cards<br />
require<br />
micro-holes<br />
to locate the<br />
probe wires.<br />
Larger wafers & more complex ICs<br />
Higher density probe cards,<br />
match coefficient of thermal expansion<br />
New materials, smaller holes, shaped holes, high accuracy<br />
<strong>Laser</strong> micro-hole drill<strong>in</strong>g<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 17
<strong>Laser</strong> <strong>Micro</strong>-hole Drill<strong>in</strong>g <strong>for</strong> Probe Cards<br />
Materials: silicon, alum<strong>in</strong>a, silicon nitride, silicon carbide, Vespal<br />
Choose high prf, pulsed visible laser <strong>for</strong> all except Vespal.<br />
For Vespal choose pulsed, high prf, deep-UV laser<br />
Hole sizes : 20 - 100 µm diameter<br />
Hole shapes : circular or elliptical, parallel or tapered<br />
For circular holes choose dedicated trepann<strong>in</strong>g head<br />
For elliptical holes choose air-bear<strong>in</strong>g XY axes or galvo mirror system<br />
Parallel/taper depends upon laser power <strong>and</strong> focuss<strong>in</strong>g geometry<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 18
<strong>Laser</strong> <strong>Micro</strong>-hole Drill<strong>in</strong>g <strong>for</strong> Probe Cards<br />
Typical examples:<br />
Material Thickness Hole Dia Drill time<br />
(mm) (mm) (s)<br />
Alum<strong>in</strong>a 0.64 0.120 15<br />
Alum<strong>in</strong>a 0.60 0.090 9<br />
SiN 0.50 0.075 9<br />
SiC 1.00 0.120 45<br />
SiC 1.50 0.200 120<br />
Vespal 0.50 0.025 0.05<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 19
<strong>Laser</strong> <strong>Micro</strong>-hole Drill<strong>in</strong>g <strong>for</strong> Probe Cards<br />
1<br />
Alum<strong>in</strong>a<br />
Cut speed<br />
vs<br />
Thickness<br />
vs<br />
<strong>Laser</strong> Power<br />
Cut Speed (mm/s)<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
0 10 20 30 40 50<br />
0.25mm<br />
0.38mm<br />
0.60mm<br />
1.00mm<br />
<strong>Laser</strong> Power (W)<br />
All holes are trepanned so cutt<strong>in</strong>g speed is most<br />
relevant to estimate process speed scal<strong>in</strong>g<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 20
<strong>Laser</strong> <strong>Micro</strong>-hole Drill<strong>in</strong>g <strong>for</strong> Probe Cards<br />
Close Packed Arrays<br />
Alum<strong>in</strong>a<br />
200 µm dia on<br />
500 µm pitch<br />
through 640 µm thickness<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 21
<strong>Laser</strong> <strong>Micro</strong>-hole Drill<strong>in</strong>g <strong>for</strong> Probe Cards<br />
System Requirements<br />
Very High Accuracy Placement of Holes<br />
Typically +/- 1.5 µm over 12 <strong>in</strong>ch wafer<br />
Air bear<strong>in</strong>g axes with l<strong>in</strong>ear motors <strong>and</strong> l<strong>in</strong>ear encoders<br />
True XY calibration us<strong>in</strong>g glass calibration plate<br />
CAD file conversion software<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 22
<strong>Laser</strong> Trimm<strong>in</strong>g of MEMS<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 23
<strong>Laser</strong> Trimm<strong>in</strong>g of MEMS<br />
Improve Yield<br />
by <strong>Laser</strong><br />
Trimm<strong>in</strong>g<br />
PASS<br />
Probe first device<br />
FAIL<br />
• MEMS<br />
• MEOMS<br />
(Photonics)<br />
Algorithm to determ<strong>in</strong>e<br />
laser trimm<strong>in</strong>g<br />
Probe<br />
next<br />
device<br />
<strong>Laser</strong> trim<br />
Probe device<br />
PASS<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 24
<strong>Laser</strong> Trimm<strong>in</strong>g of MEMS<br />
Precision Mass Removal<br />
by cutt<strong>in</strong>g, etch<strong>in</strong>g or drill<strong>in</strong>g<br />
10 g 9 g<br />
Trimm<strong>in</strong>g of MEMS such as accelerometers &<br />
angular rate sensors to “balance” device<br />
Ablated volumes <strong>in</strong> the range of 1 - 1000 µm 3 per pulse<br />
For silicon 1 µm 3 = 2.3 x10 -15 Kg = 2.3 fg<br />
But at pulse frequency of of 20kHz,<br />
removal rate <strong>in</strong> the range 46 pg - 46 ng per second<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 25
<strong>Laser</strong> Trimm<strong>in</strong>g of Other Devices<br />
Photonic Devices - trimm<strong>in</strong>g of transmissive properties<br />
- add<strong>in</strong>g Bragg grat<strong>in</strong>gs<br />
Electronic<br />
- trimm<strong>in</strong>g of resistive or capacitive<br />
properties<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 26
<strong>Wafer</strong> Process<strong>in</strong>g Systems<br />
• Active wafer-level test, repair <strong>and</strong> optimization<br />
• <strong>Wafer</strong> dic<strong>in</strong>g <strong>and</strong> micromach<strong>in</strong><strong>in</strong>g<br />
• Device trimm<strong>in</strong>g/balanc<strong>in</strong>g<br />
• Automatic prob<strong>in</strong>g<br />
• IC & MEMS devices<br />
• <strong>Micro</strong>-hole drill<strong>in</strong>g<br />
• <strong>Micro</strong>-cutt<strong>in</strong>g & dic<strong>in</strong>g<br />
•High throughput<br />
•Full wafer test capability<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 27
Conclusions<br />
<strong>Laser</strong> micro-mach<strong>in</strong><strong>in</strong>g enables probe card<br />
designers greater choice <strong>in</strong> materials <strong>and</strong><br />
flexibility <strong>in</strong> hole geometry to pursue advanced<br />
devices<br />
Comb<strong>in</strong>ed wafer prob<strong>in</strong>g <strong>and</strong> laser trimm<strong>in</strong>g<br />
enables higher yield <strong>in</strong> MEMS <strong>and</strong> other devices<br />
Ox<strong>for</strong>d <strong>Laser</strong>s June 2002 28
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