ROCHESTER INSTITUTE OF TECHNOLOGY MICROELECTRONIC

© March 24, 2008, Dr. Lynn Fuller

Gig Ohm Resistors Fabrication Process

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Rochester Institute of TechnologyMicroelectronic Engineering

ROCHESTER INSTITUTE OF TECHNOLOGYMICROELECTRONIC ENGINEERING

Gig Ohm Resistor Process Details

Dr. Lynn Fuller/Paul John Webpage: http://people.rit.edu/lffeee

Microelectronic Engineering Rochester Institute of Technology

82 Lomb Memorial Drive Rochester, NY 14623-5604

Tel (585) 475-2035 Fax (585) 475-5041

Email: [email protected] MicroE Webpage: http://www.microe.rit.edu

3-24-2008 GigOhmResistors.ppt

http://people.rit.edu/~lffeee

mailto:[email protected]

http://www.microe.rit.edu/



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INTRODUCTION

This project is to design and make Gig Ohm Resistors. The process will use ion implanted (Boron) poly silicon resistors. The design is for discrete devices of size suitable for automated pick and place surface mounting for printed circuit board assembly. The individual resistors are 2mm x 3mm and eight different designs are arranged in an array which will be cut into individual chips at the end of the process. The first run will use aluminum metal. Future runs will use a metal stack of aluminum, chrome, nickel, and solder.

Applications for resistors of this high value are MOSFET biasing of high input impedance amplifiers, charge sensors for piezoelectric (quartz) pressure sensors, and more. In these applications the exact value is not usually important.



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LAYOUT



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ALIGNMENT KEY LOCATIONS, CHIP SIZE, ETC.

Lower Left Corner =(0,0)Upper Right Corner = (9400,6400)Step Size in X = 9.6 mmStep Size in Y = 6.6 mmCenter of Die = (4700 , 3200)Location of PA alignment Mark = Center of Die = (4700,3200)B scope (Y-Direction) Fine Alignment 20P4F Island Center = 4955,3680B scope (Y-Direction) Fine Alignment 20P4F Window Center = 4955,3500C scope (X-Direction) Fine Alignment 20P4F Island Center = 4550,3700C scope (X-Direction) Fine Alignment 20P4F Window Center = 4350,3699



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PROCESS STEPS

Gig Ohm Resistor process1. ID01 scribe2. CL01 RCA clean3. OX05--- 30,000 wet oxide4. CV01 deposit poly5. IM01 – Ion Implant poly Si6. PH03 – 1 – poly7. ET08 poly etch8. ET07 strip resist9. CL01 RCA clean10. OX08 – poly reox11. CV03 – LTO

12. OX08 DS anneal13. PH03 – 2 CC14. ET10 etch CC15. ET07 strip resist16. CL01 RCA Clean, modified17. ME01 Deposit Metal18. PH03 -3- metal19. ET05 etch metal20. ET07 strip resist21. SI01 SINTER22. TE01 Test 123. SA01 Saw Wafer



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STARTING WAFER P-TYPE, 35 OHM-CM

For this project the starting silicon wafer type and resistivity is not that important because the resistors will be made of poly silicon on an insulating oxide layer. The starting wafer is only a substrate for the thin films on its surface.



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ID01 - IDENTIFY WAFER (SCRIBE WAFER)

Paul JohnD1



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RCA CLEAN

DI waterrinse, 5 min.

H20 - 50HF - 160 sec.

HPMH2O–4500mlHCL-300ml

H2O2 – 900ml75 °C, 10 min.

SPIN/RINSEDRY

APMH2O – 4500ml NH4OH–300mlH2O2 – 900ml75 °C, 10 min.



PLAYANSWER

What does RCAstand for?



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RCA CLEAN

RCA BenchSpin/Rinse/Dry Tool



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GROW 30,000 Å OXIDE

30,000 Å SiO2

Push at 800 C in N2Ramp to 1100 C in dry O2 Time = ~900 min. in wet O2Ramp down to 800 C in N2Pull at 800 C in N2

Use Recipe 430 – Tube 1



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WET OXIDE GROWTH CHART

Steam900C

1300C

0.01

0.1

1

10

101 100 1000Time in minutes

OxideThicknessin microns



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BRUCE FURNACE RECIPE 430 – WET OXIDE 30,000Å

1100°C

800 °C

Boat Out Boat In Boat OutLoad Push Stabilize Ramp-Up Soak Anneal Ramp-Down Pull

Recipe #430

800 °C

25 °C

Any0 lpmnone

800 °C

At the end of a run the furnace returns to Interval 0 which is set for boat out, 25 °C and no gas flow. The furnace waits in that state until someone aborts the current recipe or loads a new recipe.

Wet Oxide Growth, Target 30,000 Å

Interval 0 Interval 1 Interval 2 Interval 3 Interval 4 Interval 5 Interval 6 Interval 7 Interval 8

12 min 15 min 30 min 5 min 15 hrs 5 min 60 min 12 min10 lpm 10 lpm 5 lpm 5 lpm 10 lpm 15 lpm 10 lpm 15 lpmN2 N2 N2 O2 O2/H2 N2 N2 N2



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30,000 Å OXIDE GROWTH

Polysilicon, 3500A30,000 Å SiO2



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OXIDE COLOR VERSUS THICKNESS TABLEThickness Color Thickness Color

500 Tan 4900 Blue700 Brown 5000 Blue Green

1000 Dark Violet - Red Violet 5200 Green1200 Royal Blue 5400 Yellow Green1500 Light Blue - Metallic Blue 5600 GreenYellow1700 Metallic - very light Yellow Green 5700 Yellow -"Yellowish"(at times appears to be Lt gray or matellic)2000 LIght Gold or Yellow - Slightly Metallic 5800 Light Orange or Yellow - Pink2200 Gold with slight Yellow Orange 6000 Carnation Pink2500 Orange - Melon 6300 Violet Red2700 Red Violet 6800 "Bluish"(appears violet red, Blue Green, looks grayish)3000 Blue - Violet Blue 7200 Blue Green - Green3100 Blue 7700 "Yellowish"3200 Blue - Blue Green 8000 Orange3400 Light Green 8200 Salmon3500 Green - Yellow Green 8500 Dull, LIght Red Violet3600 Yellow Green 8600 Violet3700 Yellow 8700 Blue Violet3900 Light Orange 8900 Blue4100 Carnation Pink 9200 Blue Green4200 Violet Red 9500 Dull Yellow Green4400 Red Violet 9700 Yellow - "Yellowish"4600 Violet 9900 Orange4700 Blue Violet 10000 Carnation Pink

SiO2 SiO2

Yes! No!

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TENCORE SPECTRAMAP

Measure Oxide Thickness



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REFLECTANCE SPECTROMETERNANOSPEC FILM THICKNESS MEASUREMENT

INCIDENT WHITE LIGHT, THE INTENSITY OF THEREFLECTED LIGHT IS MEASURED VS WAVELENGTH

WHITE LIGHT SOURCE

OPTICS

WAFER

MONOCHROMATOR& DETECTOR

3000 Å OXIDE

7000 Å OXIDE

Oxide on Silicon 400-30,000 ÅNitride 400-30,000Neg Resist 500-40,000Poly on 300-1200 Ox 400-10,000Neg Resist on Ox 300-350 300-3500Nitride on Oxide 300-3500 300-3500Thin Oxide 100-500Thin Nitride 100-500Polyimide 500-10,000Positive Resist 500-40,000Pos Resist on Ox 500-15,000 4,000-30,000



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STEP ETCH APPARATUS

BUFFERED HF

Lower 1/4 inch every 45 seconds



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ETCH STEPS IN OXIDE ON C1

5000 Å

BARE SILICON



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DEPOSIT LPCVD POLY SILICON

Polysilicon, 3500ALPCVD, 610C, ~45min

30,000 Å SiO2



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DOPE POLY SILICON BY ION IMPLANT

Polysilicon, 3500A

30,000 Å SiO2

50kEV, Boron, B11 from BF3 gasDose ~1e12

Wafer 1 Dose =Wafer 2 Dose =Wafer 3 Dose =Wafer 4 Dose =



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VARIAN 350 D ION IMPLANTER (4” AND 6” WAFERS)



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B11 IMPLANT FOR BORON THRESHOLD ADJUSTS, STOP, P-WELL

I µA

50

40

30

10

20

ION MASS (AMU)

30191110 4948

B10

B11

BF2

BF+

USE THIS PEAK

PLAY



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PHOTO 1 RESISTOR

Polysilicon, 3500A

30,000 Å SiO2

Coat with ~1.0µm Photoresist



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COAT PHOTORESIST ON SSI TRACK

COAT.RCP



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EXPOSE RESIST ON CANON STEPPER

i-Line Stepper = 365 nmNA = 0.52, = 0.6Resolution = 0.7 / NA = ~0.5 µm20 x 20 mm Field SizeDepth of Focus = k2 /(NA)2

= 0.8 µm



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DEVELOP RESIST ON SSI TRACK

Polysilicon, 3500A

30,000 Å SiO2



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ETCH POLY SILICON ON LAM 490


Use Lam 490Recipe FACPOLYSF6 140 sccmO2 40 sccmGap 1.5 cmPower 140 watts325 mTorr150 Sec/wafer



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STRIP PHOTORESIST ON BRANSON ASHER




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RCA CLEAN


H20 - 50HF - 160 sec.


H2O2 – 900ml75 °C, 10 min.

SPIN/RINSEDRY




PLAYANSWER

What does RCAstand for?



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OXIDE REGROWTH


500A recipe 250



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LPCVD LTO


4000A LTOOr4000A TEOS + Densify



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PHOTO – 2 CONTACT CUTS




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EXPOSE

i-Line Stepper = 365 nmNA = 0.52, = 0.6Resolution = 0.7 / NA = ~0.5 µm20 x 20 mm Field SizeDepth of Focus = k2 /(NA)2

= 0.8 µm



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ETCH CONTACT CUTS




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STRIP RESIST

Branson Asher



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MODIFIED RCA CLEAN


H20 - 50HF - 160 sec.


H2O2 – 900ml75 °C, 10 min.

H20 - 50HF - 160 sec





SPIN/RINSEDRY



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DEPOSIT METAL

CVC 601 Sputter Tool



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PHOTO - 3 - METAL



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SSI COAT AND DEVELOP TRACK FOR 6” WAFERS

SSI coat and develop track



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ASML 5500/200

NA = 0.48 to 0.60 variable= 0.35 to 0.85 variable With Variable Kohler, orVariable Annular illuminationResolution = K1 /NA = ~ 0.35µm

for NA=0.6, =0.85 Depth of Focus = k2 /(NA)2

= > 1.0 µm for NA = 0.6i-Line Stepper = 365 nm

22 x 27 mm Field Size



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ETCH METAL

Wet Etch



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STRIP RESIST

Branson Asher



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SINTER

Native Oxide

Before Sinter After Sinter

Reduce Surface States

Reduce Contact Resistance

OxygenHydrogen, neutral region

Silicon Crystal

+ charge region Silicon DiOxideInterfacesilicon

atom that lostan electron



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PICTURES



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TEST

R = 1/slope = 106 Gigohms

Rhos = 106 50/1800 = 2.94 Gigohms/square



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TEST

R=1/slope; Rhos=R / #sqs; Rho=Rhos x thickness (3500Å); Dose=implanter setting

R wafer 4 = 106 G ; Rhos = 2.94 Gohm/sq; Rho = 103K ohm-cm; Dose=1E12 cm-2R wafer 3 = 339 G ; Rhos = 9.42 Gohm/sq; Rho = 330K ohm-cm; Dose = ?R wafer 2 = 943 G ; Rhos = 26.2 Gohm/sq; Rho = 917K ohm-cm; Dose = ?R wafer 1 = 1104 G; Rhos = 30.7 Gohm/sq; Rho = 1075K ohm-cm; Dose = ?



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SAW WAFER



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SUMMARY

A process has been created.



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REFERENCES

1. Silicon Processing for the VLSI Era, Volume 1 – Process Technology, 2nd, S. Wolf and R.N. Tauber, Lattice Press.

2. The Science and Engineering of Microelectronic Fabrication, Stephen A. Campbell, Oxford University Press, 1996.



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HOMEWORK – GIG OHM RESISTORS

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ROCHESTER INSTITUTE OF TECHNOLOGY MICROELECTRONIC