Processing and Characterization of PMSSQ Based Materials for Nanoporous Low-K Dielectrics

Transcription

1 Processing and Characterization of PMSSQ Based Materials for Nanoporous Low-K Dielectrics P. Lazzeri 1, L. Vanzetti 1, M. Bersani 1, M. Anderle 1, J.J. Park 2, Z. Lin 2,, R.M. Briber 2, G.W. Rubloff 2, R.D. Miller 3 1 ITC-irst, v. Sommarive 18, Povo, Trento, Italy 2 University of Maryland, 2145 A.V. Williams Building College Park, MD 3 IBM Almaden Research Center, San Jose, CA

2 Device Shrinkage and Interconnect Delay Increased line resistance and capacitive coupling Interconnect delay dominates overall circuit delay Al / 2 Cu / Low K Low K materials (organic, silica based materials) Nano porous low K materials 2 (K = 4.0) Low k (k ~ 2.0) Al (ρ 3.0 µω cm) Cu (ρ -1.7 µω cm) Nanoporous PMSSQ Low polarizability matrix (K ~ 2.7) Nano porous low K (K 2.0) Low water uptake (<1%), thermal stability, mechanical strength.

3 Strategy for Nanoporous Low K Matrix Porogen RT Thermal Cycle 450 C Spin on (Solution) Matrix cross link, Nano phase separation Porogen Volatilization Fully cured Cross link Nanopores Characterizing surface and bulk - ToF SIMS -XPS Characterizing volatile product -TDMS (Thermal Desorption Mass Spectrometry) Compare surface to gas phase Compare precursor recipe - Low H and high H PMSSQ

4 Thermal Reaction Goal Matrix cross link Porogen release RT T, t Max 450 C

5 Nanoporous PMSSQ Materials Matrix material Porogen materials Backbone 1.5 PMMA DMAEMA unit: contains N PMSSQ PMMA-co-DMAEMA Methyl group Non-polar, hydrophobic and space-occupying Hydroxyl group Cross linking of matrix Tertiary amino group Hydrogen bonding with H in Matrix Miscibility between matrix and porogen

6 Low K film Processing low-k matrix resin (PMSSQ) porogen (PMMA co-dmaema) solvents 450 C, 2Hrs Rpm = 3000 Time = 20 sec Thickness ~ 1 µm initial cure template formation final cure ToF SIMS Static-SIMS kev) Surface Spectroscopy, Surface Imaging Pseudo-Dynamic SIMS (sputtering by Cs+) Depth Profiling XPS TDMS Matrix cross linking Heat Thermal decomposition of porogen material Material fingerprint and molecular structure Degree of polymerization Thermal behavior of porogen material Interaction between matrix and porogen Matrix precursor chemistry effect Designing nanoporous low K materials for electrical performance

7 x10 5 PMSSQ Finger Print Analysis SSIMS, negative SI x n intensity 5.0 n 4.0 cleavage of the parent ion (i.e. by loss of 2 ) n=0 n=1 n=2 3.0 n=1 n= Peak assignments are well matched 200 to experimental 400 results. 600 mass Compression Factor : 52 Peaks PMSSQ are + regularly 50 spaced C x 3 by a monomer unit. Fragmentation pattern depends on chemical structure and is sensitive to cross linking.

8 Precursor Chemistry x SSIMS, negative SI x700 Low H PMSSQ n x SSIMS, negative SI High H PMSSQ x amu H n intensity 4.0 intensity 0.6 Twin peaks Compression Factor : mass Compression Factor : mass Mass spectrum of high H PMSSQ has a twin peak near the key species with mass difference 1.98 amu by replacing group with H group. [H] high ~ 2 * [H] low

9 Polymerization of High H PMSSQ Intensity Cross linking reaction ToF-SIMS Major crosslinking 100 C 200 C Remaining crosslinking 46C3H9 57C5H15 69C5H15 710C7H21 812C7H21 913C9H Temperatrure [ C] Intensity [amp] H 2 desorption product TDMS Mass spectrometer 1.50E-08 MASS( 18 ) 1.10E E E E Temperature [ C] Water signal from pure PMSSQ Major crosslinking C, completed at 450 C. Dehydration occurs as H groups crosslinks.

10 High H vs. Low H RELATIVE INTENSITY Low H High H 58C5H15 610C5H TEMPERATURE [ C] RELATIVE INTENSITY RELATIVE INTENSITY High H Low H 47C3H9 47C3H TEMPERATURE [ C] High H Low H 711C7H21 813C7H TEMPERATURE [ C] Small size fragments Large size fragments High H PMSSQ crosslinks faster than low H PMSSQ. Reaction rate depends on the concentration and proximity of H end groups.

11 Porogen : Surface Analysis (XPS) High H As deposited Fully cured Photoemission Intensity (a.u.) 0% Porogen 30% Porogen Backbone (C-H) DMAEMA (C-N) C 1s Photoemission Intensity (a.u.) 0% Porogen 30% Porogen C 1s Binding Energy (ev) Binding Energy (ev) Porogen related components : Backbone and DMAEMA Porogen materials completely volatilized at T = 450 C

12 Porogen : Surface Analysis 1.4 ToF SIMS Porogen in High H matrix 1.2 PMMA ( ) RELATIVE INTENSITY DMAEMA (CN) TEMPERATURE [ C] DMAEMA ligand : Cleavage and evolution 225 C C (90%) Remaining material desorbs by > 325 C PMMA ligand : No apparent transformation until > 325 C Backbone : Behavior follows that of PMMA ligand No porogen agglomeration observed in high H matrix.

13 Porogen : Gas phase analysis Intensity [amp] 3.00E E E E E-08 H 3 C DMAEMA ligand CH C H 2 C CH 2 N MASS( 58 ) Intensity [amp] 7.00E E E E E E-09 PMMA and backbone Backbone MASS( 85) PMMA MASS( 100 ) 5.00E-09 H 3 C 1.00E E+00 Temperature [ C] 225 C 325 C 0.00E+00 Temperature [ C] 225 C 325 C 350 C 450 C Mass spectrometer detected fragment of DMAEMA (mass 58) and PMMA parent ion (mass 100). The decomposition temperature range for DMAEMA is 225 C ~ 325 C,and PMMA 350 C ~ 450 C. Good agreement with ToF SIMS result.

14 Thermal Behavior of Nanoporous PMSSQ High -H Low H Porogen backbone PMMA Matrix cross link DMAEMA T [ C]

15 Conclusion ToF SIMS, XPS, and TDMS were used to analyze the thermal behavior of porogen-containing PMSSQ Polymerization kinetics of PMSSQ Matrix Polymerization of PMSSQ was observed mainly at 100 C 200 C, and water was detected as a byproduct by mass spectrometry Rate of polymerization depends on the concentration of H functional groups: high H PMSSQ shows faster polymerization Porogen behavior upon thermal processing Porogen materials decompose at higher temperatures than PMSSQ polymerization temperatures ( > 225 C) DMAEMA and PMMA thermally decompose at different temperatures (225 C 300 C, PMMA and backbone > 325 C)

16 Particles Containing Porogen Materials (AVS 02 Denver) imaging ToF-SIMS, negative SI PRGEN AGGLMERATES 225 C < curing < 450 C agglomerate density depends on curing T agglomerate composition (PMMA/DMAEMA ligand/backbone) depends on curing T Field of view: 10.0 x 10.0 µm 2 2 µm Porogen particles are observed only in low H PMSSQ film. Slow cross linking process of low H PMSSQ allows diffusion of porogen material. Low concentration of H with less hydrogen bonding with DMAEMA does not hinder phase separation.