WAFER DICING ( An introduction to the Process )
Presented By : MANISH CHOPRA September 13 , 2007 Continental Device India Limited 1 Process Engineer
1 What is Process ?
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2 INPUT OUTPUT Process
RESOURCES
“ Any activity or set of activities that uses resources to transform inputs to output can be considered as Process” September 13 , 2007 Continental Device India Limited 3
3 Type of Semiconductor manufacturing flow • Front end (Wafer fabrication ) • Back end (Assembly, Test and Packaging)
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4 Front End
• The "front-end" is wafer processing which is performed in a Wafer Fab area. • A Fab is one of the most complex industrial facilities to be found anywhere. A state-of-the-art Fab, costing over $1 billion. • It has the cleanest environment in the world - many times cleaner than the best hospital operating theater. • The process of wafer fabrication is a series of 16-24 loops, each putting down a layer on the device.
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5 Major steps in Front end process
Wafer preparation
Oxidation
Photolithography
Diffusion
Deposition
Metallization
Passivation
Back Grinding September 13 , 2007 Continental Device India Limited 6
6 Back End Process
• The "back-end" is Test, Assembly and Packaging, where the finished wafer is split up into individual die (chips) which are then assembled into packages which can be handled in the final applications.
• Full functional Electrical test is performed at both wafer and package level to ensure outgoing quality
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7 Major steps involved in Back End Process
Wafer Probing Die singulation (Dicing) Die Bonding Wire Bonding Molding Lead finish Trim Form Electrical Testing Marking September 13 , 2007 Continental Device India Limited 8 Packing
8 Wafer Dicing / Wafer Singulation
Process of reducing a wafer containing multiple identical (Die) chips to dice . In our Process , a 4’’ wafer gives up to 100 k Devices . Kiru
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9 DICING is not a Cake walk!
Process Critical Parameters
30000 RPM Spindle Revolution 25 mil Exposure of Blade Exposure 1 mil Blade Thickness Work piece (Wafer ) Thickness of 8 mil 100 k die / wafer
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10 5 W’s & 1 H (DICING PROCESS) • What • When •Why •Who • Where •How
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11 Turtle diagram - Elements of a Process
RESOURCES CONTROLS
OUTPUT INPUT Dicing Process
METHOD KEY CRITERIA chip (HOW)
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12 RESOURCES(WHAT) 1. DAD321 DICING SAW 2. DIAMOND BLADE 3. MYLAR 4. FRAME 5. DI WATER 6. COMPRESSED AIR 7. NITROGEN 8. IONISER 9. TEFLON / VACCUM TWEEZER 10. MICROWASHER September 13 , 2007 Continental Device India Limited 13 Back Next
13 PROCEDURE(HOW)
1. TECHNIQUES
2. DICING PROCESS FLOW
3. METHOD
Next
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14 KEY CRITERIA
1. SEPERATION OF DIE WITH REQUIRED DIMENSION FROM WAFER 2. YIELD MONITORING(THROUGHPUT) 3. CUT QUALITY 4. COST TO PROCESS back
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15 CONTROL
1. M/C CONTROL
2. SPC
Back
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16 M/C Control
• Programmable stopping of machine (based on requirement) for online inspection of product.
• Monitoring through Camera.
CONTROL
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17 INPUT
DIFFUSED WAFER
BACK
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18 OUTPUT
DICED WAFER OR SINGULATED WAFER
Back
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19 CHIP Good Die Bad Die
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20 Conversions
• 1 mil = 25.4 um
• 1 um =0.040 mil
• 1 inch=25.4 mm=25400 um=1000mil
• 1 mm =40mil
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21 Nomenclature in DICING
Kerf
Scribe Path
Chip
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22 Nomenclature in Dicing
• Scribe path- Thin non-functional spacing in between the functional parts of the chips, where a saw can safely cut the wafer without damaging the chip.
• Dicing tape (Mylar) is a PVC sheet with synthetic adhesive on one side to hold both the wafer frame and the wafer.
BACK
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23 Nomenclature in Dicing Wafer frame may be made of plastic or metal, but it should be resistant to warping, bending, corrosion, and heat.
Kerf width is defined as the average width of the cut line plus the error attributed to micro chipping.
Note :The singulated dice may be left attached to the wafer tape for pick-and-place during die attach or may be individually kept in waffle packs for future assembly. September 13 , 2007 Continental Device India Limited 24 Back Turtle
24 DICING TAPE CONSTITUENTS
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25 DAD 321
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26 DAD 321 Specifications
Users perform workpiece loading, alignment and unloading manually.
Auto-alignment
Air driven Spindle
Vaccum Chuck
Online monitoring
Auto stopping as per Program
Workpiece size - 4,5,6 inch
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27 Blade Nomenclature
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28 Dicing Blade
• A diamond blade is a ring composed of abrasive grits (diamond particles) held together by a binder - either nickel or phenolic resin or metal-powder sintering.
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29 Parameters for Selecting a Blade ¾ Choosing the right binder
¾ Diamond selection
¾ Dressing
After Dressing Before Dressing
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30 Blade Tradeoff
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31 Blade Sharpening action
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32 Blade which we are using? • Disco Blade: Turtle NBC – ZH –1 04 F –SE - K44 - 27H D C B Series Kerf width Aluminium Hub 0.8-1.0 mil
Blade Exposure Grit Concentration 20-25 mil low Conc. Grit size Code Grit Size: Mesh size=3000 Mesh size # 3000 Size=2/6 um Size # 2/6 um I.D=19.05mm O.D=55.56mm Brittle Bond Low Backside Chipping Sharp Edge Hub type Customized Inspection September 13 , 2007 Continental Device India Limited 33
33 Techniques
– Scribing and Breaking
– Mechanical sawing (Dicing Saw)
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34 Application characteristics
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35 Cost of Process
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36 Process Flow Wafer DICING
Mounting Full-Cut Dicing Return Dicing tape is The dicing saw dices The wafer is applied to the the wafer to Die returned to the backside of wafer singulation cassette.
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37 Elements in Wafer Dicing
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38 Method • Application of tape to the backside of Wafer.
• Setting up the wafer on the Dicing Saw chuck.
• Selecting the cutting program for the device.
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39 Method Checking the blade status.
Aligning the wafer in both the channels.
Execute the cutting.
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40 Method
• Remove the Diced Wafer from Chuck.
• Clean the Diced Wafer using Micro wash. NEXT
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41 DICING PROGRAM • MACHINE AND DEVICE PARAMETERS THAT CAN AFFECT THE DICING PROCESS:- • CRITICAL MACHINE PARAMETERS:- 1.Air pressure--85-120psi 2.DI water pressure--40-100psi 3.N2 pressure--30-100psi 4.DI water conductivity--<0.2uS 5.Room temp = +/- 2 degree Celsius.
6.SpindleSeptember 13 , 2007 r.p.m-30000rpm Continental Device India Limited 42
42 DEVICE PARAMETERS:- 1.Work size (wafer diameter) 2.Work thickness (wafer thickness) 3.Chip size 4.Tape thickness Blue mylar-2.8-3.0mil white mylar-4.5-5.0mi 5..Blade height For Blue myler-0.0013-0.0020inch For white myler-0.0030-0.0035inch 6.Feed rate(cut speed)-3inch/s BACK
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43 Issues affecting wafer mounting process / DICING
1.Air bubbles between Mylar and wafer.
2.Metal mounds at back surface of wafer.
3.Wrinkles in Mylar
4.Wafer cracked in grinding
5.Foreign particles between wafer and Mylar. September 13 , 2007 Continental Device India Limited 44
44 Issues affecting wafer mounting process / DICING 6.Non uniform back surface
7.Particles on the mounting chuck
8.Warpage
9. Inadequate mounter temperature
10. Weak adhesion of tape September 13 , 2007 Continental Device India Limited 45
45 Effects of wafer mounting Process on Dicing
– Chips fly off during dicing and microwash.
– Chip loss
– Crack at the time of fixing the wafer in dicing machine.
– Blade breakage.
– Back or front side chipping.
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46 Why Dressing?
• To smoothen the exposed diamond grits of blade radially for fine quality cut.
• To check the effect of loading of substrate on blade.
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47 Dressing Program on Dresser Board
Dresser board:-
Material - Silicon Carbide Grit size - 30 microns Thickness - 1mm
Depth of cut – 22 mils Feed Rate No. of cuts 5 mm/sec 2 at 30,000 rpm 10mm/sec 2 at 30,000 rpm
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48 Precutting
•Smoothen the exposed Diamond grits •Minimising the Loading effect . September 13 , 2007 Continental Device India Limited 49
49 DEFECTS OF DICING PROCESS
• Chip cracks. • Chipping (Front or back) • Misalignment. • Silicon Dust. • Light / Deep cut. • Chips fly off. • Multiples. • Blade breakage. • Mylar residue.
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50 DICING DEFECTS
Fronside Chipping Misalignment
Multiples September 13 , 2007 Continental Device India LimitedTorn Mylar 51
51 DICING DEFECTS
Backside Chipping
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52 Chipping
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53 Chipping – Front side and Back side
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54 Backside Chipping
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55 Defects criteria Front side defects criteria
Cracking / Chippings / Misalignment distant less than 2.5 microns (0.098 mils) from any active area.
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56 September 13 , 2007 Continental Device India Limited 57
57 FRONT SIDE CHIPPING MEASTT
DICING STREET
CHIPPING
FRONT SIDE CHIPPING MEASTT ***
DICING CUT
Front Side Sawing Defects
General Defects criteria :-
1. Cracking / Chippings / Misalignment distant less than 2.5 microns (0.098 mils) from any active area. --- FRONT SIDE CHIPPING MEASTT *** 2. Dice not 100% sawn through. 3. Any peeling, corrosion, delamination ,or other Gross defects in Passivation, metal or other layer. 4. Stains or holes due to Silicon particles originated during the sawing operation which can affect Functionality or Reliability.
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58 Back Side Sawing Defects Criteria Chipping criteria w.r.t. Wafer Thickness
WAFER THICKNESS CHIPPING MAX (Y Axis) 75-110um (2.95-4.33 mils) 30um (1.18 mils) 110-150um (4.33-5.91 mils) 40um (1.57 mils)
150-200um (5.91-7.87 mils) 50um (1.97 mils) 200-300um (7.87-11.81 mils) 70um (2.76 mils) 300-400um (11.81-15.75 mils) 100um (3.94 mils) > 400um (15.75 mils) 125um (4.92 mils)
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59 BACK SIDE CHIPPING MEASTT
DICING STREET
BACK SIDE CHIPPING
"b"
"a"
DICING CUT
BACK SIDE CHIPPING = (b-a) { As shown in figure above}
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60 September 13 , 2007 Continental Device India Limited 61
61 Backside Chipping
Accept Reject
TURTLE September 13 , 2007 Continental Device India Limited 62
62 DICING AND GRINDING PROCESS IMPACT ON DEVICE RELIABILITY
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63 Some facts on Grinding and Dicing
• Grinding Process adds a large amount of stress to the wafer. • The stress is released by subsequent chemical process. • After that also there are some stress left . • Stress can cause Defects (Chipping and Chip cracks ) during Dicing.
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64 CHIPPING / CHIP CRACKS ARE VERY CRITICAL FOR DEVICE FUNCTIONALITY AND RELIABILITY . So these defects should be addressed very carefully during processing of wafer. TURTLE
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65 SPC
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66 SPC on Kerf width Measurement
KERF WIDTH Vertical to cut Horizontal to cut DATE WAFER NO. M/C NO. T C B L R T C B L R 3/7/07 9066-13 7 1.2 1 1.1 1 1.2 0.9 1 1.1 1.2 1
KERF WIDTH CHART (VERTICAL)
1.50 1.40 XDBAR+3*S (1.38) 1.30 XDBAR+2*S(1.31) XDBAR+1*S(1.24) 1.20 XDBAR(1.17) 1.10 XDBAR-1*S(1.1) XDBAR-2*S(1.03) 1.00 XDBAR-3*S(0.96) 0.90 0.80 3/7/07 4/7/07 5/7/07 6/7/07 7/7/07 10/7/07 11/7/07 12/7/07 13/7/2007 14/7/2007 17/7/2007 18/7/2007 19/7/2007 20/7/2007 21/7/2007 24/7/2007 25/7/2007 26/7/2007 27/7/2007 28/7/2007 31/7/2007 Kerf Width should be less than 1.4 mil
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67 KERF WIDTH Vertical to cut Horizontal to cut DATE WAFER NO. M/C NO. T C B L R T C B L R 3/7/07 9066-13 7 1.2 1 1.1 1 1.2 0.9 1 1.1 1.2 1
KERF WIDTH CHART (HORIZONTAL)
1.40
1.30 XDBAR+3*S(1.28) 1.20 XDBAR+2*S(1.21) XDBAR+1*S(1.14) 1.10 XDBAR(1.07) 1.00 XDBAR-1*S(1.0) XDBAR-2*S(0.93) 0.90 XDBAR-3*S(0.86) 0.80 3/7/07 4/7/07 5/7/07 6/7/07 7/7/07 10/7/07 11/7/07 12/7/07 13/7/2007 14/7/2007 17/7/2007 18/7/2007 19/7/2007 20/7/2007 21/7/2007 24/7/2007 25/7/2007 26/7/2007 27/7/2007 28/7/2007 31/7/2007
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68 BACK SIDE CHIPPING
NO. OF DIES INSPECTED - 20 dies / wfr
VERTICAL MEASTT (um) WAFER NO. TOP CENTER BOTTOM LEFT RIGHT AVERAGE RANGE 1 NX15PO2V - 19 4.65 13.96 11.63 9.31 6.98 9.306 9.31
MOVING RANGE CHART FOR BACK CHIPPING Average (VERTICAL MEASTT) Range
25 a 20 15 10 5 Av e r age & R 0 XF47S022-40 XF47S022-26 W545JL82-01 W545JL82-24 W5518081-01 W5518081-25 W5518071-01 W5518071-25 W5519191-01 W5519191-25 W551L141-01 W551L141-25 W544X901-01 W549N041-01 W549N041-25 W549N081-01 W549N081-25 W550JNX1-01 W550JNX1-25 NX15PO2V - 19 NX15PO2V - 01 NX15PO2V Wafer No.
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69 HORIZONTAL MEASTT (um) WAFER NO. TOP CENTER BOTTOM LEFT RIGHT AVERAGE RANGE 1 NX15PO2V - 19 12.77 17.03 14.9 10.65 12.77 13.624 6.38
MOVING CHART FOR BACK CHIPPING Average (HORIZONTAL MEASTT) Range
18 16 14 12 10 8 6 4 Average & Range & Average 2 0 XF47S022-40 XF47S022-26 W545JL82-01 W545JL82-24 W5518081-01 W5518081-25 W5518071-01 W5518071-25 W5519191-01 W5519191-25 W551L141-01 W551L141-25 W544X901-01 W549N041-01 W549N041-25 W549N081-01 W549N081-25 W550JNX1-01 W550JNX1-25 NX15PO2V - 19 NX15PO2V - 01 NX15PO2V Wafer No.
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70 FRONT SIDE CHIPPING TREND NO. OF DIES INSPECTED - 20 dies / wfr
VERTICAL MEASTT (um) WAFER NO. TOP CENTER BOTTOM LEFT RIGHT AVERAGE RANGE 1 NX15PO2V - 19 18.61 23.26 16.28 13.96 18.61 18.144 9.3
Average MOVING RANGE FOR FRONT CHIPPING (VERTICAL MEASTT.) Range
25
20
15
10
Average & Range & Average 5
0 40 W545 W544 W549 W549 W551 W551 W550 W551 W551 - 19 JL82-24 8081-25 8071-25 9191-25 L141-25 X901-01 N041-25 N081-25 JNX1-25
NX15PO2V XF47S022- Wafer No.
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71 HORIZONTAL MEASTT (um) WAFER NO. TOP CENTER BOTTOM LEFT RIGHT AVERAGE RANGE 1 NX15PO2V - 19 17.03 12.76 12.77 14.90 17.03 14.898 4.27
MOVING RANGE CHART FOR FRONT CHIPPING Average (HORIZONTAL MEASTT) Range
25
g 20
15
10
Average & Ran 5
0 40 W545 W544 W549 W549 W551 W551 W550 W551 W551 - 19 JL82-24 8081-25 8071-25 9191-25 L141-25 X901-01 N041-25 N081-25 JNX1-25 NX15PO2V XF47S022- Wafer No.
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72 Learning's / Experiences
• Water Flow rate optimization • Chilled DI water project. • First cut direction • UV tape for Dicing. • Blue Mylar Concept. • Ionizer Concept. • Zig for removing periphery die.
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73 THANK YOU
KIRU
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