Effect of Annealing and Passivation on the Electromigration and Linewidth Dependence
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etch and two cascade D.I. water rinses. The dielectric, phosphosilicate glass (PSG), was deposited with the Novellus Concept One PECVD system. The deposition was performed by generating a RF plasma operating at 13.56MHz. The PSG film with 5.7wt.% phosphorus and a thickness of 6KA was deposited at 2.2Torr using 1KW total power. 8KA AICu(1%)Si(I%) metal was deposited using a Varian 3190 cassette to cassette DC magnetron sputtering system. The sputtering sources of this tool were of mini-QuantumTM gun configuration. The deposition process conditions were; 325 0C preheat followed by a 300 0 C deposition temperature and 7.5mTorr chamber argon pressure. The deposition was completed using a single station regime and the substrates were cooled under vacuum for 15 seconds prior to unloading. Samples were patterned using positive photoresist over an organic anti-reflective coating layer to eliminate any possibility of reflective notching of the photoresist lines. Metal etching was then performed in a single wafer LAM 4620 RIE system using standard BCI 3 and C1 chemistries. Approximately I000A of the oxide sublayer was removed during the overetch of the metal lines. To minimize any corrosion potential, the LAM 4620 system utilizes a separate chamber for ashing the wafers prior to exposing them to atmosphere followed by hot N 2 and a hot deionized water rinse. Wafers at this point were removed from the etch system and processed in a Semitool spray acid etch tool for an ethylene glycol/ammonium fluoride, hydrofluoric acid etch targeted to remove between 300-400A of oxide. The oxide etch selectively removes any further "veils" or chlorine residues from the etched Al lines. A final Semitool amine based solvent rinse was used to remove any remaining organic residues. After Al deposition and patterning, a matrix was employed using the controlling factors of: anneal/no anneal and passivation/no passivation, as listed in Table I. The substrates were annealed in a cantilevered mini-brute furnace stack at 430'C for 30 minutes in forming gas (95% N 2, 5% H2). The samples which received both anneal and passivation, received the anneal prior to passivation. The passivation process was completed in the Novellus Concept One PECVD system. The passivation was deposited at 2.2Torr with IKW total power. The phosphorus concentration of the PSG passivation was 4.Owt.% and had thickness of 8 KA. Passivated Non-Passivated Annealed
2 samples
2 samples
Non-annealed
2 samples
2 samples
Table I. Matrix to study effect of anneal and passivation on microstructure and electromigration. Stress was measured on all wafers before and after each processing step by a Flexus 5200. The stress values were generated by measuring the radius of curvature of the substrate prior to and after deposition. The stress value was calculated by using eq.l: ft2
_ýS
a (stress)
(__s_
)
(eq. 1)
1
2
6,f
__R
_(e•l
where E, is Young's modulus of Si substrate (1.3Oxl0 5 MPa), % is Poisson's ratio of Si substrate (0.279), ts is Si substrate thickness, R, and Rf are t
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