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Dry Etching of Copper Using Plasma. Kejun Xia Semiconductor TCAD Lab. Auburn University, AL Oct 19, 2003. Outline. Background Introduction > Why Copper & low k for IC Interconnection > Some methods of getting fine copper lines Halogens Plasma Etching > Chlorine Plasma Etching

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dry etching of copper using plasma

Dry Etching of Copper Using Plasma

Kejun Xia

Semiconductor TCAD Lab.

Auburn University, AL

Oct 19, 2003

outline
Outline
  • Background Introduction

> Why Copper & low k for IC Interconnection

> Some methods of getting fine copper lines

  • Halogens Plasma Etching

> Chlorine Plasma Etching

> Basic problems and solutions

> Chlorine-Argon Plasma Etching

> Using Iodine-containing substance

questions
Questions
  • What’s the function of Argon in Chlorine-Argon plasma etching?
  • Why is the process gas preferable in some case to detect the starting and ending point other than CuCl when using Optical Emission Spectroscopy Process monitoring ?
introduction
Introduction
  • Interconnection, The veins of ICs

> line RC delay prevail over gates delay

  • For today’s technology node and beyond, Aluminum is no longer suitable

> relatively high resistance (2.66um-Ohm)

> Electromigration

electromigration
Electromigration

Hillock formation Whisker bridging Accumulation

& depletion

http://www.mse.berkeley.edu/groups/doyle/serdar/RESEARCH/copper.pdf

how about copper low k
How about Copper/low k

INTERCONNECT OF NEW MILLENNIUM: COPPER

BY SERDAR AKSU, FALL 1999

sem pictures of cu interconnection
SEM pictures of Cu interconnection

http://www.mse.berkeley.edu/groups/doyle/serdar/RESEARCH/copper.pdf

ways to get fine cu lines
Ways to get fine Cu lines
  • Subtractive etch

Dry etching using Chlorine Plasma

Main problem is low rate, improved with several methods

  • Damascene (CMP)

Currently used

Unavailable when feature size down to 0.1um

  • Thermally Produce the CuO, then etch it away with an organic acid (hfacH)

High etching rate of CuO, 1um/min at 423K

Low rate of oxidation and the incompatibility with plasma

Chlorine Plasma’Copper Reaction in a New Copper Dry Etching Process

Journal of The Electrochemical Society, 148 ~9! G524-G529 ~2001

chemical mechanical polish
Chemical Mechanical Polish

Single/dual Damascene

Presently used

Difficult when feature size down to 0.1um

http://www.mse.berkeley.edu/groups/doyle/serdar/RESEARCH/copper.pdf

dry etching system
Dry Etching system

http://www.ifm.liu.se/~petas/mikrosystem/Lectures/Lectures_files/L2Dryetching.pdf

main difficulty in etching cu with chlorine plasma
Main Difficulty in Etching Cu with Chlorine plasma

CuClx,

the main reaction product, has a low volatility.

morphology of cuclx as a function of chlorine plasma process parameters
Morphology of CuClx as a function of Chlorine Plasma process parameters

Journal of The Electrochemical Society, 148 ~9! G524-G529 ~200112-20

slide13
Time

1 min 2 min

at 25 0C, 20mTorr, 600W, Cl2 20sccm.

Grain size and porosity increases with time

because of ion bombardment

ppt:13-21Journal of The Electrochemical Society, 148 ~9! G524-G529 ~2001

slide14
Time

CuClx remain increasing by enhancement of Cl

pressure
Pressure

20mTorr 100mTorr

Ion bombardment play an important role

pressure1
Pressure

The thickness of CuClx decreases becoz of ion bombardment, but

Why should Cathode Self-Biased Voltage drop with increasing pressure?

The ratio of cathode area to anode area increases.

power
Power

300W 600W

Higher etching rate

power1
Power

Vsc=(VRF)pp/2-Vp

substrate temperature1
Substrate temperature

Why has a peak for CuClx ? Below 150oC, Cl transport rate and reaction rate increase; Above 150oC, Evaporation of CuClx dominates.

how to remove cuclx
How to remove CuClx ?
  • High substrate temperature

473-523K required in order to adequately remove this product. Thus it seems this will not be used for the sake of thermal budget in ICs fabrication.

  • High density plasma source,

Adding Argon

  • Ultraviolet, Infrared or laser
chlorine argon plasma for cu etching
Chlorine-Argon plasma for Cu etching

Comparison of etching rate between with and without Argon

Russian Microelectronics, Vol. 31, No. 3, 2002, pp. 179–192. Translated from Mikroelektronika, Vol. 31, No. 3, 2002, pp. 211–226.

role of argon
Role of Argon
  • Accelerate bulk generation of atomic chlorine by electron-impact dissociation

Cl2+Ar(3P0,3P1,3P2)-->Cl+Cl+Ar

  • Accelerate removal of reaction products from surface active centers under the action of incident ions and UV photons
process monitoring by optical emission spectroscopy oes
Process monitoring by Optical Emission Spectroscopy (OES)

435.8nm CuCl band at different temperatures

ultraviolet light irradiation assisted low temperature cu etching
Ultraviolet Light Irradiationassisted Low temperature Cu etching

http://mirine.kaist.ac.kr/research/cu_1.html

desorbed gas species in different cuclx
Desorbed gas species in different CuClx

Not all of the component desorbed

schematic of icp with a collimated uv lamp 300 400nm
Schematic of ICP with a collimated UV lamp (300-400nm)

http://mirine.kaist.ac.kr/research/cu_1.html

etching rate with power
Etching rate with Power

Etching rate is approximately five times higher than that without UV

Journal of The Electrochemical Society, 146 (8) 3119-3123 (1999)

effects from polycrystalline characteristic of copper during plasma etching
Effects from Polycrystalline characteristic of copper during plasma etching

200nm width copper lines with a granulated surface

http://www.infotech.tu-chemnitz.de/~zfm/eng/research/fokum.html

2 ion channeling effect in plasma etching
(2) Ion Channeling Effect in plasma etching

Etching rate 2 Larger than

Etching rate 1, consequently

Etching deviates from

the vertical direction.

sem pictures of ion channeling
SEM pictures of Ion channeling

Dark area is <110>plane which has a least atomic density.

In the case of multilayer interconnection, this is greatly harmful

Decrease uniformity

Decrease etching selectivity

Dry Etching Considerations for Copper Metallizations V.V.Makarov, et dl, NPTest Inc., 150 Baytech Dr. San

Jose, CA D.P.Griffis, P.E.Russell, North Carolina State University, 1010 Main Campus Dr. Raleigh, NC

one solution
One Solution
  • preliminary ion bombardmentation beam incidence different from normal, so that grains showing strongest channeling and therefore most resistive for etching under normal ion bombardment are effectively amorphized/etched. (short time)

Without ion preliminary bombardment With ion preliminary bombardment

using iodione containing substances for copper etching
Using Iodione-containing substances for copper etching
  • CH3I+HI using RF or DC discharge.
  • CuI has a high volatility
  • High etching rate. 60nm/min at 353K.

Hampden-Smitch, M.J. and Kodas, T.T., Copper Dry Etching:

New Chemical Approaches, Mater.Res.Bull,1996,no.6,p.39

conclusion
Conclusion
  • Cu/low k interconnection has its great advantage
  • CuClx has a low volatility. Ion bombardment and UV photon can assist to remove CuClx at room temperature.
  • Chlorine-Argon plasma has a higher etching rate than Chlorine plasma itself.
answers
Answers
  • What’s the function of Argon in Chlorine-Argon plasma etching?

Do favor to increase the concentration of atomic Chlorine; Accelerate removal of products With bombardment.

answers1
Answers

Why is the process gas preferable in some case to detect the starting and ending point other than CuCl?

CuCl has a low saturated pressure at room temperature, thus can not be detected accurately by OES.