Fraunhofer IZM Workshop November 25, 2002 Thin Semiconductor Devices

Transcription

1 Fraunhofer IZM Workshop November 25, 2002 Thin Semiconductor Devices

2 Effect of Wafer-Thinning Processes On Ultra-Thin Wafer and Die Strength Tony Schraub Ph.D.

3 A Cooperative Program between Three US Companies Strasbaugh Grinding & Polishing Tru-Si Technologies Dry Plasma Etching Saint-Gobain (Norton) Abrasive grind wheels Die Strength Testing

4 Thin Die Strength Dependency Stress-concentrating flaws due to sub-surface damage by grind forces on abrasive grits Damage removal method and amount Final thickness of each process step Edge condition (die and wafer edge chips) Handling stress during and between process steps Die size, shape and grind line orientation Brittle fracture test method This program addresses only items in yellow

5 Variables tested in this Program Amounts Removed: (all wafers final thickness 100 um) Coarse Grind ~625um Fine Grind 20 um Grind + No polish or Etch Grind +Polish 5 um Grind+ Polish 10 um Grind + Etch 5 um Grind + Etch 10 um Grind + Etch 25 um 350 mesh 350 mesh # 2000 YES none none YES YES None # 8000 YES YES YES YES YES YES

6 Previously Presented Die Strength Vs. Silicon Removal W. Kroninger, Infineon Technologies Grind and 10 µm Dry Etch Grind and 10 µm Wet Etch Rel. Die Strength in N Grind Only DBG Grind and 3 µm Polish Silicon Removal Method Source: IZM Conference 2001

7 Test Result Summary Die Strength 2000 Grit Grind 8000 Grit Grind Grind & Polish Grind & ADP Etch

8 How Was Test Done? Bare 200mm (1,0,0) Wafers Thinned to 100µm 1. Grind Only 2. Grind and Polish 3. Grind and Dry Plasma Etch (ADP) Dice Wafers into 32 Die 25mm X 25mm Measure all 32 Individual Die Fracture Loads

9 Wafer back grinder Strasbaugh 7AF (ntellect) Key Strasbaugh Technologies: In-Situ Thickness Measurement Linear Traversing Grind Spindles Innovative Abrasive grind wheels Force Adaptive Grinding

10 Saint Gobain FAVSTM grinding wheels Key Norton Technologies: Range of specifications engineered to suit applications In depth R&D and application support to develop best processes

11 Tru-Si Atmospheric Downstream Plasma (ADP) Key Tru-Si Technologies: Atmospheric Dry Chemical Etch Thinning & Damage Removal Thru-Silicon Connections NoTouch Handling

12 Die Fracture Load Method Biaxial flexture test on 25mm by 25mm die Pin-on-ring fixture on MTS test machine 12mm steel ball onto 16mm Diameter ring Ground side of die put in tension Tape (compressive side) holds fragments Load rate at 0.5mm/minute

13 MTS Material Test Tool (15.9 mm) MOVEABLE CROSSHEAD M T S F R A M E RING FIXTURE PIN FIXTURE WAFER M T S F R A M E LOAD CELL MTS FRAME

14 Strengthen Wafer/Die by Removing Grinding Damage Sub surface damage Surface damage

15 Remove Subsurface Damage to Increase Strength After Grinding After ADP Etching

16 Examples of Die Fractures Fractured at High Load Fractured at Low Load Fractured at Medium Load

17 Weibull Curve Test Results Weibull Comparison of Grind, Polish, & ADP Etch Probability LN(LN(1-p)) Fracture Load (lbs) LN (Fracture Load [lbs]) 2000 Grind 8000 Grind 5um Polish 10um Polish 5um ADP 10um ADP

18 Mean Fracture Loads (Pounds) % improved die fracture load using #8000 without any treatment Grind 8000 Grind 5um Polish 10um Polish 5um ADP 10um ADP

19 Raw Test Results Die Strength Die Fracture Load in Pounds Grind 5um Polish 5um ADP Die Strength Sorted from Lowest to Highest

20 Comparisons of Min, Mean, and Max Min, Mean, & Max Comparisons Die Fracture Load in Pounds Grind um Polish um ADP 14.1 Min Mean Max

21 Strength Comparison with Different Amounts of Etch Strength Equivalent after 5um ADP Etch Probability LN(LN(1-p)) Fracture Load (lbs) 5um ADP 10um ADP 25um ADP LN (Fracture Load [lbs])

22 Fracture Load vs.thickness No correlation of die strength with die thickness within the thickness range observed within the wafer 5 micron polished 10 micron ADP dry etch Fracture Load (lbs) Fracture Load (lbs) Thickness (µm) Thickness (µm)

23 #2000 Grit vs #8000 Grit with ADP: Mean Fracture Load (Lbs) % improvement % improvement Etching 5 um after grinding with the #8000 gives better strength than etching 10 um after grinding with the # Grit 5um ADP Etch 8000 Grit 5um ADP Etch 2000 Grit 10um ADP Etch 8000 Grit 10um ADP Etch

24 Conclusions 8000 Grit Grind better than 2000 Grit Grind. The strength of the dies ground with the #8000 is better than the ones ground with #2000 Polishing or ADP Etching after grinding significantly strengthen die ADP Etching after #8000 fine grind produced the Strongest Die

25 Future Direction for Ultra thin Examine Wafer Level Strength For example: Effect of rounded edges from ADP Etching on wafer strength

26 Contact Information Strasbaugh Tru-Si Saint-Gobain Abrasives Die Strength 2000 Grit Grind 8000 Grit Grind Grind & Polish Grind & ADP Etch

27 Additional Information Acknowledgements Test data summary Other suggestions for future work Equipment descriptions 8000 Grind wheel information

28 Test Data Summary Test Case Test Case Description Die Thickness (µm) Die Fracture Load (lbs) Fine Wheel Polish microns removed ADP Etch microns removed Min Mean Max Range Stdev Min Mean Max Range Stdev 1A A A A A B A A B B

29 Large increases in die strength with enhanced surface treatments Percentage Increase in Strength Over 2000 Grit Grind 3500% 3034% 3000% 3034% 2500% 2000% 1582% 1650% 1500% 1582% 964% 1000% 49% 31% 500% 0% 49% Max Mean 8000 Grind 5um Polish 5um ADP Min

30 Other Suggestions for Future Work Ultra-thin-wafer Dicing method influence Data for thinner wafers below 100 µm thickness Optimize grind recipes for new #8000 wheel Optimize each process removal amounts Smaller die; Rectangular die Whole wafer strength evaluations, including edge effects Polish after etching and/or etching after polishing Study great increase in range of die strength after polish or etch 2.5 µm polish removal data (to complement 5 and 10 µm)

31 Acknowledgements This work is a cooperative effort of these companies & individuals: Tony Schraub, Ph.D Consultant on thin wafers Sal Kassir Grinding R&D Engineer, Strasbaugh Bryan Vogt Polishing Process Engineer, Strasbaugh Sam Kao, Ph.D R&D Applications, Tru-Si Technologies Frank Kretz,Manager--Atmospheric Downstream Plasma Equipment, Tru-Si Technologies Jeri Ikeda, Ph.D R&D, Saint-Gobain Abrasives Rama Vedantham Saint-Gobain Abrasives Thomas Puthanangady Saint-Gobain Abrasives

32 Tru-Si Enables 50 Micron and Below Etching Wafer Etching Equipment Dry Chemical Etch Atmospheric Operation Applications: Grind Damage Removal Rough Wafer Backsides Damage Free Dicing Selective Film Etching Thin Wafer Handling Equipment NoTouch end Effectors and Wands for thin bowed, bumped wafers

33 #8000 Fine Grinding Wheel Designed and manufactured by Saint-Gobain Abrasives Supplied by Strasbaugh as part number # Ultra fine grind wheel with 1-2 micron diamond grits Produces stronger wafers with less bow than <2000 wheels Improved surface finish to Angstroms