CMPChemical Mechanical

PlanarizationCarried out by Eran Cantrell, Bobby O’Ryan,

And Maximus (CMP)

OBJECTIVES-Increase removal rate

- Invent a way to roughen pad surface

- Measure effect of roughening on removal rate and uniformity

- Measure effect of slurry flow rate on removal rate and uniformity

- Reach conclusion of how to better maintain machine efficiency

Background-The CMP (Chemical Mechanical

Planarization) process polishes silicon wafers, using slurry (liquid sandpaper) and a platen (polishing pad) to prepare the wafers for lithography. This requires the wafers to be as smooth and uniform

as possible.This process is affected by the slurry flow rate, the pad roughness, pressure on the

wafer, the platen spin rate, and the length of time the wafer is polished.

Equipment Description

• Load Polish Unload Clean Load

• Uses Air, N2, DIW, Slurry, Water, Electricity

Control Box

Carrier

Primary Polish Platen

Slurry Delivery Arm

Cleaning Station

ControlMe

Wafer Boat

Load Station

Final Slurry Pump

Primary Slurry Pump

Final Polish Platen

Wafer Boat

Polishing Arm

Unload Station

Experimental Conditions

• Five conditions were set up. This was to test the impact of two variables, while keeping all else constant: the slurry flow rate,

and the pad roughening.

• Conditions were set up from low SFR (75 ml/min) and low PR (30 sec), increasing to high SFR (225 ml/min) and high PR (2 min). The standard was 150 ml/min of flow rate, and 1 min of

roughening.

• The CRPM (carrier rotations per min) rate stayed 50 rpm constant.

• The platen stayed at 30 rpm when polishing, 60 rpm when roughening.

• Polishing time was 30 sec constant.

The mass and thickness of the wafers were measured before and after to determine which method was removing the most

material.

DataAverage Uniformity

0.992

0.993

0.994

0.995

0.996

0.997

0.998

0.999

S-H R-H S-H R-L S-L R-H S-L R-L standard

Polish Condition

Ave

rag

e U

nifo

rmity

Average Uniformity

DataRemoval Rate Scatter Plot

1150.00

1200.00

1250.00

1300.00

1350.00

1400.00

1 3 5 7 9 11 13 15

Wafer

Rem

ova

l Rat

e (A

/min

)

• Each colored line represents the average of the closest three data points surrounding it. While you can see an up-down variation between averages, if you look at the individual data it is impossible to tell the groups apart.

DataAverage Removal Rate

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

S-H R-H S-H R-L S-L R-H S-L R-L standard

Polish Condition

Avera

ge R

em

oval

Rate

(A

/min

)

Average Removal Rate

Recommendations for Future Work

•Roughening technique should be more mechanical, and methodical.

•Develop a technique to measure pad roughness.

Conclusion•Pad roughening appears to increase

the removal rate of the silicon dioxide film, and improves wafer

uniformity.

•Due to confidence interval overlap, an optimal roughening time cannot

be selected.

•Similar conclusions can be made about slurry flow rate.

Acknowledgements• We would like to thank Jason Hower, for his

tutoring throughout this process;

• Dr. Milo Koretsky, for his helpful advice;

• Maximus, who endured our unorthodox methods;

• All the companies who have donated materials (Intel and Sumco);

• And the rest of the SESEY staff, for all the support and funding (and effort) they have

provided for the students.