1、AVS 2002 Nov 3 - Nov 8, 2002 Denver, Colorado INTEGRATED MODELING OF ETCHING, CLEANING AND BARRIER COATING PVD FOR POROUS AND CONVENTIONAL SIO2 IN FLUOROCARBON BASED CHEMISTRIES*,Arvind Sankaran1 and Mark J. Kushner2 1Department of Chemical Engineering 2Department of Electrical and Computer Engineer
2、ing University of Illinois, Urbana, IL 61801, USA email: asankarauiuc.edu mjkuiuc.edu http:/uigelz.ece.uiuc.edu,*Work supported by SRC, NSF and SEMATECH,University of Illinois Optical and Discharge Physics,AGENDA,Low dielectric constant materialsSurface reaction mechanism and validation Fluorocarbon
3、 etching of SiO2/Si Ar/O2 etching of organic polymerHigh aspect ratio etching of porous and non porous SiO2 Integrated Modeling: Ar/O2 strip of polymer and IMPVDConcluding Remarks,AVS03_AS_02,University of Illinois Optical and Discharge Physics,LOW DIELECTRIC CONSTANT MATERIALS,The increase in the s
4、ignal propagation times due to RC delay has brought the focus onto low dielectric constant (low-k) materials (inorganic and organic),AVS03_AS_03,Inorganics such as porous silica (PS) are etched using fluorocarbon chemistries; organics are etched using oxygen chemistries.,University of Illinois Optic
5、al and Discharge Physics,GOAL FOR INTEGRATED MODELING,Plasma processing involves an integrated sequence of steps, each of which depends on the quality of the previous steps.,CFDRC_0503_05,University of Illinois Optical and Discharge Physics,SURFACE REACTION MECHANISM - ETCH,CFx and CxFy radicals are
6、 the precursors to the passivation layer which regulates delivery of precursors and activation energy.Chemisorption of CFx produces a complex at the oxide-polymer interface. 2-step ion activated (through polymer layer) etching of the complex consumes the polymer.,AVS03_AS_05,Activation scales as 1/L
7、 and the L scales as 1/bias.In Si etching, CFx is not consumed, resulting in thicker polymer layers.Si reacts with F to release SiFx.,University of Illinois Optical and Discharge Physics,SURFACE REACTION MECHANISMS - STRIP,AVS03_AS_06,Ar/O2 is typically used for polymer stripping after fluorocarbon
8、etching and resist removal. Little polymer removal is observed in absence of ion bombardment suggesting ion activation.,For SiO2 etching in mixtures such C4F8/O2, the fluorocarbon polymer is treated as an organic. Resists are treated similarly.,University of Illinois Optical and Discharge Physics,MO
9、NTE CARLO FEATURE PROFILE MODEL (MCFPM),The MCFPM predicts time and spatially dependent profiles using energy and angularly resolved neutral and ion fluxes obtained from equipment scale models. Arbitrary chemical reaction mechanisms may be implemented, including thermal and ion assisted, sputtering,
10、 deposition and surface diffusion. Energy and angular dependent processes are implemented using parametric forms.,INTELTALK_AS_17,Mesh centered identity of materials allows “burial”, overlayers and transmission of energy through materials.,University of Illinois Optical and Discharge Physics,MODELIN
11、G OF POROUS SILICA,MCFPM may include “two phase” materials characterized by porosity and average pore radius.Pores are incorporated at random locations with a Gaussian pore size distribution. Pores are placed until the desired porosity is achieved with/without interconnects.,AVS03_AS_07,Interconnect
12、ed structures can be addressed.,University of Illinois Optical and Discharge Physics,TYPICAL PROCESS CONDITIONS,Process conditions Power: 600 W Pressure: 20 mTorr rf self-bias: 0-150 V C4F8 flow rate: 40 sccmThe fluxes and energy distributions are obtained using the HPEM.,AVS03_AS_08,University of I
13、llinois Optical and Discharge Physics,BASE CASE ION AND NEUTRAL FLUXES,Self-bias = - 120 V. Decrease in neutral and ion fluxes along the radius have compensating effects.,AVS03_AS_09,Ions have a narrow energy and angular distribution, in contrast to neutrals.,University of Illinois Optical and Disch
14、arge Physics,VALIDATION OF REACTION MECHANISM: C4F8,The mechanism was validated with experiments by Oehrlein et al using C4F8, C4F8/Ar and C4F8/O2.1Threshold for SiO2 etching was well captured at self-bias -40 V. Polymer formation is dominant until the threshold biasAs polymer thins at higher biases
15、, the etching proceeds.,AVS03_AS_10,1 Li et al, J. Vac. Sci. Technol. A 20, 2052, 2002.,University of Illinois Optical and Discharge Physics,VALIDATION: C4F8/Ar and C4F8/O2,Larger ionization rates result in larger ion fluxes in Ar/C4F8 mixtures. This increases etch rates. With high Ar, the polymer l
16、ayers thins to submonolayers due to less deposition and more sputtering and so lowers etch rates.O2 etches polymer and reduces its thickness. Etch rate has a maximum with O2, similar to Ar addition.,AVS03_AS_11,University of Illinois Optical and Discharge Physics,PROFILE COMPARISON: MERIE REACTOR,AV
17、S03_AS_12,Process conditions Power: 1500 W CCP Pressure: 40 mTorr Ar/O2/C4F8: 200/5/10 sccm,V. Bakshi, Sematech,University of Illinois Optical and Discharge Physics,VALIDATION OF POROUS SiO2 ETCH MODEL,Two porous substrates 2 nm pore radius, 30% porosity 10 nm pore radius, 58% porosityProcess condit
18、ions Power: 1400 W (13.56 MHz) Pressure: 10 mTorr rf self-bias: 0-150 V 40 sccm CHF3Etch rates of P-SiO2 are higher than for NP-SiO2 due to lower mass densities of P-SiO2.,AVS03_AS_13,Exp: Oehrlein et al, J. Vac. Sci.Technol. A 18, 2742 (2000),University of Illinois Optical and Discharge Physics,WHA
19、T CHANGES WITH POROUS SiO2?,The “opening” of pores during etching of P-SiO2 results in the filling of the voids with polymer, creating thicker layers. Ions which would have otherwise hit at grazing or normal angle now intersect with more optimum angle.,INTELTALK_AS_30,An important parameter is L/a (
20、polymer thickness / pore radius).,Adapted: Standaert, JVSTA 18, 2742 (2000),University of Illinois Optical and Discharge Physics,EFFECT OF PORE RADIUS ON HAR TRENCHES,AVS03_AS_15,With increase in pore radius, L/a decreases causing a decrease in etch rates.Thicker polymer layers eventually lead to ma
21、ss corrected etch rates falling below NP-SiO2. There is little variation in the taper.,4 nm,16 nm,10 nm,University of Illinois Optical and Discharge Physics,HAR PROFILES: INTERCONNECTED PORES,INTELTALK_AS_40,60%,100%,0%,Interconnectivity,University of Illinois Optical and Discharge Physics,EFFECT OF
22、 PORE RADIUS ON CLEANING,AVS03_AS_17,Larger pores are harder to clean due to the view angle of ion fluxes.Unfavorable view angles lead to a smaller delivery of activation energy, hence lower activated polymer sites.,4 nm,16 nm,ANIMATION SLIDE,Ar/O2=99/1, 40 sccm, 600 W, 4 mTorr,University of Illinoi
23、s Optical and Discharge Physics,CLEANING INTERCONNECTED PORES,CHEME_AS_19,Cleaning is inefficient with interconnected pores. Higher interconnectivity leads to larger shadowing of ions.,60%,100%,0%,ANIMATION SLIDE,Interconnectivity,Ar/O2=99/1, 40 sccm, 600 W, 4 mTorr,University of Illinois Optical an
24、d Discharge Physics,EFFECT OF ASPECT RATIO ON STRIPPING,AVS03_AS_19,Cleaning decreases with increasing aspect ratios.Pores at the top of the trench are stripped better due to direct ions (view angle).Pores near the bottom see ions reflected from the bottom of the trench and are cleaned better.,3,5,1
25、,ANIMATION SLIDE,Aspect Ratio,Ar/O2=99/1, 40 sccm, 600 W, 4 mTorr,4 nm,16 nm,NP,10 nm,University of Illinois Optical and Discharge Physics,EFFECT OF PORE RADIUS ON Cu DEPOSITION,AVS03_AS_20,Surrogate study for seed layer deposition and barrier coating.,Larger pores require longer deposition times fo
26、r conformal coverage.This produces thicker bottom and open field films.Voids are created or initiated by larger pores.,University of Illinois Optical and Discharge Physics,EFFECT OF INTERCONNECTIVITY ON Cu IMPVD,AVS03_AS_21,Interconnected pores need to be sealed to avoid pin-hole formation.Pore seal
27、ing by Cu IMPVD ineffective at larger interconnectivities.Thicker layers to seal pores produces trench narrowing, which can lead to pinch off.,30%,100%,0%,60%,Interconnectivity,University of Illinois Optical and Discharge Physics,CONCLUSIONS,Etching of PS obeys scaling laws as that of SS. Etch rate
28、increases for smaller pores and slows for larger pores (at high porosities).L/a determines etch rate variation of P-SiO2. Polymer filling increases the net thickness.Stripping is inefficient for interconnected pore networks and for larger pores due to the unfavorable view angles for the ion fluxes. Low aspect ratio pores are better cleaned. Cu IMPVD is non-conformal for closed pore networks with larger pores. Pin-hole formation and trench narrowing is seen for interconnected networks.,AVS03_AS_22,
