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 > Basic problems and solutions > Chlorine-Argon Plasma Etching > Using Iodine-containing substance
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 • 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 Hillock formation Whisker bridging Accumulation & depletion http://www.mse.berkeley.edu/groups/doyle/serdar/RESEARCH/copper.pdf
How about Copper/low k INTERCONNECT OF NEW MILLENNIUM: COPPER BY SERDAR AKSU, FALL 1999
SEM pictures of Cu interconnection http://www.mse.berkeley.edu/groups/doyle/serdar/RESEARCH/copper.pdf
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 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 http://www.ifm.liu.se/~petas/mikrosystem/Lectures/Lectures_files/L2Dryetching.pdf
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 Journal of The Electrochemical Society, 148 ~9! G524-G529 ~200112-20
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
Time CuClx remain increasing by enhancement of Cl
Pressure 20mTorr 100mTorr Ion bombardment play an important role
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 300W 600W Higher etching rate
Substrate temperature 25oC 250oC
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 ? • 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 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 • 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) 435.8nm CuCl band at different temperatures
Ultraviolet Light Irradiationassisted Low temperature Cu etching http://mirine.kaist.ac.kr/research/cu_1.html
Desorbed gas species in different CuClx Not all of the component desorbed
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 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 200nm width copper lines with a granulated surface http://www.infotech.tu-chemnitz.de/~zfm/eng/research/fokum.html
(1) Higher reaction rate at the grain boundary Result in unsmooth profile
(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 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 • 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 • 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 • 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 • 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.
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.