Optical Emission Analysis ofCF4/CHF3/Ar Plasma Etch of Oxide

Anjali Walia

Irvington High School

8/13/15

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RIE : Reactive Ion Etch

• Type of dry etching

• Chemically reactive plasmaremoves material deposited on on wafers

• Plasma created by applying strong RF field

• Electrons accumulate on platen -> - DC self Bias

• Plasma sheath has positive charge

• Positive ions drift toward wafer platen and react with surface

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Centura MxP

• Magnetically enhanced RIE chamber

• Cathode receives RF power

• Rotating magnetic field applied -> more ionized, reactive gas

• Magnetic field decreases DC bias by lowering resistance of plasma

• Channels distribute He across back of wafer -> prevents photoresist reticulation

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CF4/CHF3/Ar etching

C

F

F

F

F

F

F

H

F

Si substrate

PR PR

SiO2

OO

C

• F reacts with SiO2 -> O2 becomes a part of the etch

• C forms teflon-like polymer that is attacked by O2

• Polymerizes over non-O2 bearing surfaces4

Optical Emission Spectroscopy

• Method of chemicalanalysis

• Intensity of light emittedfrom spark at particularwavelength used to determine relative quantities of elements in plasma

• Wavelength -> identity of element

• Intensity proportional to number of atoms of element

• Used to obtain spectrum of etch process5

Optical Setup

• Ocean Optics spectrometer with range195 – 900 nm

• Ocean Optics software for spectrum

• 2 meter Fiber Patch Cable from Thorlabs with range 200-1200 nm

Centura MXP

Fiber

Spectrophotometer

LaptopUSB

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Test Structure

• 2 main sets of tests: Oxide Etch and Spacer Etch

• Different wafers run for each set: 10 μ SiO2/Si

1 μ SiO2/Si

PR/Si

Thin PR(DUV 210 - 0.6)/10 μ SiO2/Si

PR(OiR 906 - 12)/1 μ SiO2/Si

• Ran O2 Clean process on a Bare Si wafer before and after each test to clean the chamber

• Each process run for 10 minutes

• Scans every 10 milliseconds 7

Standard Etch Profiles

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Relevant Wavelength Data

Species Wavelength

O2 (O) 437, 497, 502, 533, 544, 615, 616, 646, 700, 725, 777

N2 337, 326, 331, 390, 391, 428, 576, 580, 655, 662, 671, 688, 727, 790

Ar 451, 485, 550, 603, 697, 707, 750, 416

F 624, 635, 641, 677, 683, 686, 687, 690, 691, 697, 714, 713, 720, 733, 740, 743, 751, 755, 757, 761 776, 780

CO2 288, 290, 337

CO 484

CF4 (CF) 240, 256

SiF4 (SiF) 640, 777

CH4 (CH) 431

C4F8 (CF2) 249, 252, 246, 255, 260, 263, 271, 275, 288, 292, 321

CN 359, 386, 387, 418, 420, 422, 647, 693, 709, 785

NO 237, 245, 256, 268, 272, 286

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< 350 nm -> overwhelmed by CF / polymerization reactions

Ar peak

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Relevant Wavelength Data

Species Wavelength

O2 (O) 437, 497, 502, 533, 544, 615, 616, 646, 700, 725, 777

CO2 288, 290, 337

CO 484

CF4 (CF) 240, 256

SiF4 (SiF) 640, 777

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Suggested Further Tests

• Rerun spacer etch on PR patterned oxide, test for polymerization after 4 minutes

• Testing of nitride films to see if they cross contaminate between etches, specifically low stress nitride and stoichiometric silicon nitride

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Thanks for listening!

Special Thanks To…

• Ryan Rivers

• Jayss Marshall

• Jesse

• Cheryl

• Marilyn

• Bill Flounders

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Works Cited

• Centura MxP manual

• P5000 Endpoint Manual

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Optical Model

• Created model to correct for loss of intensity through fiber

• Used dataset for optical fiber from Thorlabs to approximate attenuation coefficients for spectrometer output

• Back calculated to find input intensity using the known output intensity and percent transmittance

• No effect on dataset

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