Zhen-Cheng Wu

Physical and Electrical Characteristics of F- and C-Doped Low Dielectric Constant Chemical Vapor Deposited Oxides

This work compares the physical and electrical properties of two species of inorganie low dielectric constant (low-k) chemical vapor deposited (CVD) oxides, F-doped fluorinated silicate glass (FSG, k = 3.5) and C-doped organosilicate glass (OSG, k - 2.9), Experimental results indicate that FSG has a higher thermal stability (>600°C) than OSG (500°C), based on the results of thermal annealing for 30 min in an N 2 ambient. The degradation of the low-k property in OSG is mainly due to the thermal decomposition of methyl (-CH 3 ) groups at temperatures above 500°C. For the Cu gated oxide-sandwiched low-k dielectric metal-insulator-semiconductor (MIS) capacitors. Cu penetration was observed in both FSG and OSG after the MIS capacitors were bias-lemperature stressed at 250 and 150°C, respectively, with an effective applied field of 0.8 MV/cm. Specifically, Cu appeared to drift more readily in OSG than in FSG, presumably because OSG has a more porous and less dense structure than FSG. The Cu permeation can he impeded by a thin nitride (SiN) harrier layer.

Physical and Electrical Characteristics of Methylsilane- and Trimethylsilane-Doped Low Dielectric Constant Chemical Vapor Deposited Oxides

This work investigates the physical and electrical properties of two species of inorganic C-doped low dielectric constant (low-k) chemical vapor deposited (CVD) organosilicate glasses (OSGs, α-SiCO:H). They are both deposited by plasma-enhanced CVD (PECVD) processes using methylsilane [(CH 3 )SiH 3 , 1 MS]- and trimethylsilane [(CH 3 ) 3 SiH, 3 MS]-based gases as the reagents. and are designated as OSGI and OSG2, respectively, Experimental results indicate that the thermal stability temperature of OSG1 is 500°C, while that of OSG2 is 600°C, based on the results of thermal annealing for 30 min in an N 2 ambient. The deterioration of the low-k property in OSG1 is predominately duc to the thermal decomposition at temperatures above 500°C of methyl (-CH 3 ) groups, which are introduced to lower the density and polarizability of OSGs. For the Cu-gated oxide-sandwiched low-k dielectric metal-insulator-semiconductor (MIS) capacitors, Cu permeation was observed in both OSG1 and OSG2 after the MIS eapacitors were bias-temperature stressed at 150°C with an effective applied field of 0.8 MV/cm. Moreover, Cu appeared to drift more readily in OSGI than in OSG2. presumably hecause OSGI has a more porous and less cross-linked structure than OSG2. The Cu penetration can he mitigated by a thin nitride dielectric barrier.

Improvement in Leakage Current and Breakdown Field of Cu-Comb Capacitor Using a Silicon Oxycarbide Dielectric Barrier

This work investigates in the first place, the improvement in leakage current and breakdown field of the copper metal-insulator-semiconductor (Cu-MIS) capacitor with a plasma-enhanced chemical vapor deposited (PECVD) amorphous silicon oxycarbide (α-SiCO, k = 3.7) dielectric barrier. This is followed by investigating the improvement in leakage current and breakdown field of the Cu-comb capacitor with a carbon-doped low-k PECVD organosilicate glass (k = 3) as the intermetal dielectric and an α-SiCO dielectric film as the Cu cap barrier. The leakage current and breakdown field of Cu-MIS and Cu-comb capacitors are dependent on the species of the dielectric barrier. The Cu-MIS and Cu-comb capacitors with an α-SiCO dielectric barrier exhibit a leakage current at least three orders of magnitude smaller than those with an amorphous silicon carbide (α-SiC, k = 4.4) dielectric barrier at an applied electric field of 1.6 MV/cm between 25 and 250°C. Moreover, the breakdown field of the Cu-MIS and Cu-comb capacitors with an α-SiCO dielectric barrier, measured at 200°C, are 60 and 25%, respectively, higher than that of the capacitors with an α-SiC barrier. The decreased leakage current and increased breakdown field of the Cu-MIS and Cu-comb capacitors with an α-SiCO dielectric barrier are attributed to the higher density, oxygen-improved film property, non-semiconductor behavior, and lower fringe- or surface-electric field of the α-SiCO dielectric film.

Electrical Reliability Issues of Integrating Thin Ta and TaN Barriers with Cu and Low‐K Dielectric

This work investigates the integration of very thin sputtered Ta and reactively sputtered TaN barriers with Cu and a low‐dielectricconstant (low‐K) layer of poly(arylene ether) (PAE‐2). It is found that Cu readily penetrates into PAE‐2 and degrades its dielectric strength in metal‐insulator semiconductor capacitors of Cu/PAE‐2/Si structure at temperatures as low as 200°C. Very thin Ta and TaN films of 25 nm thickness sandwiched between Cu and the low‐K dielectric served as effective barriers during a 30 min thermal annealing at temperatures up to 400 and 450°C, respectively. We propose a failure mechanism of outgassing induced gaseous stress of PAE‐2 under the Ta film to explain its premature barrier degradation. The TaN barrier did not suffer from this gaseous stress problem because of its stronger adhesion to PAE‐2 than that of Ta to PAE‐2, leading to a better long‐term reliability.

Physical and Barrier Properties of Amorphous Silicon-Oxycarbide Deposited by PECVD from Octamethylcyclotetrasiloxane

This work investigates the thermal stability and physical and barrier properties for three species of amorphous silicon-oxycarbide (a-SiCO) dielectric barrier films, deposited by plasma-enhanced chemical vapor deposition (PECVD), to copper (Cu) diffusion using octamethylcyclotetrasiloxane precursor and helium (He) carrier gas with and without oxygen (O 2 ) reaction gas. The α-SiCO dielectric barrier film deposited by PECVD without O 2 reaction gas exhibits a low k-value of 2.8, thermally stable at temperatures up to 550°C, excellent moisture resistance, and superb Cu barrier property until 400°C. With the addition of O 2 reaction gas during the dielectric deposition process, the dielectric constant of the α-SiCO dielectric barrier films increases with increasing flow rate of O 2 reaction gas. Increasing flow rate of O 2 reaction gas during the deposition of the α-SiCO dielectric barrier films also degrades the thermal stability and moisture resistance of the dielectric barrier films. Moreover, the addition of O 2 reaction gas also results in a degraded Cu barrier property of dielectric films.

Physical and Barrier Properties of Plasma Enhanced Chemical Vapor Deposition α-SiC:N:H Films

In this work, we investigate the thermal stability and physical and barrier properties of three species of plasma enhanced chemical vapor deposition (PECVD) α-SiC:N:H silicon carbide films with different carbon and nitrogen contents and dielectric constants less than a value of 5.5. For comparison, one species of α-SiN:H film with a k value of 7.2 is also studied. It is found that the dielectric constant decreases with increasing content of carbon and decreasing content of nitrogen in the α-SiC:N:H film. All of the three species of α-SiC:N:H and the one species of α-SiN:H films are thermally stable at temperatures up to 500°C. However, degraded barrier capability and moisture resistance were observed for the α-SiC:N:H film with a k value of 3.5, which has a C/Si atomic ratio of 0.875. This is presumably due to the poorly crosslinked molecular structure and porosity enhancement caused by the abundant amount of carbon in the α-SiC:N:H film.

Leakage mechanism in Cu damascene structure with methylsilane-doped low-K CVD oxide as intermetal dielectric

This letter investigates the leakage mechanism in the Cu damascene structure with methylsilane-doped low-k CVD organosilicate glass (OSG) as the intermetal dielectric (IMD). The leakage between Cu lines was found to be dominated by the Frenkel-Poole (F-P) emission in OSG for the structure using a 50-nm SiC etching stop layer (ESL). In the structure using a 50-nm SiN ESL, the leakage component through SiN also made a considerable contribution to the total leakage in addition to the bulk leakage from trapped electrons in OSG. An appropriate ESL of sufficient thickness is essential to reduce the leakage for application to a Cu damascene integration scheme.This letter investigates the leakage mechanism in the Cu damascene structure with methylsilane-doped low-k CVD organosilicate glass (OSG) as the intermetal dielectric (IMD). The leakage between Cu lines was found to be dominated by the Frenkel-Poole (F-P) emission in OSG for the structure using a 50-nm SiC etching stop layer (ESL). In the structure using a 50-nm SiN ESL, the leakage component through SiN also made a considerable contribution to the total leakage in addition to the bulk leakage from trapped electrons in OSG. An appropriate ESL of sufficient thickness is essential to reduce the leakage for application to a Cu damascene integration scheme.

Dielectric and barrier properties of spin-on organic aromatic low dielectric constant polymers FLARE and SiLK

This work investigates the dielectric and barrier properties of two species of organic aromatic low dielectric constant (low-k) polymers, namely, FLARE and SiLK. Experimental results indicate that both of the low-k polymers exhibit acceptable thermal stability with respect to a thermal annealing at 400°C for 8 h in an N 2 ambient. Moreover, they show a good dielectric barrier property against Cu penetration under bias-temperature stressing (BTS) at 150°C with an applied effective field of 0.8 MV/cm. Nevertheless, an anomalous instability of the capacitance-voltage curve was observed for the first time under BTS. This finding is explained by the proposed model of stress induced dielectric polarization charges within these organic aromatic polymers. The polarization instability may seriously degrade the long term reliability of cireuit operations.

TDDB Reliability Improvement of Cu Damascene with a Bilayer-Structured α-SiC:H Dielectric Barrier

This work investigates the thermal stability and physical and barrier characteristics of two species of amorphous silicon carbide dielectric films: the nitrogen-containing α-SiCN film with a dielectric constant of 4.9 and the nitrogen-free α-SiC film with a dielectric constant of 3.8. The time-dependent-dielectric-breakdown (TDDB) lifetime of the Cu damascene metallization structure is greatly improved by using an α-SiCN/α-SiC bilayer dielectric stack as the barrier layer. This improvement is attributed to the lower leakage current of α-SiC, absence of nitridation on the Cu surface, and better adhesion of a-SiC on Cu and organosilicate glass intermetal dielectric. Although the α-SiC film has a very low deposition rate, the α-SiCN/α-SiC bilayer dielectric is a favorable combination for the barrier layer because α-SiCN can protect α-SiC from plasma attack, such as O 2 plasma attack during photoresist stripping and organosilicate plasma attack during organosilicate glass deposition.

TDDB reliability improvement in Cu damascene by using a bilayer-structured PECVD SiC dielectric barrier

This work investigates the thermal stability and barrier characteristics of two species of silicon carbide dielectric films, /spl alpha/-SiCN with a dielectric constant of 4.9 and /spl alpha/-SiC with a dielectric constant of 3.8. The TDDB lifetime of Cu damascene metallization structure is greatly improved by using a /spl alpha/-SiCN//spl alpha/-SiC bilayer dielectric stack as the etching stop layer (ESL). This improvement is presumably due to the /spl alpha/-SiC dielectrics lower leakage current, absence of nitridation on Cu surface, and better adhesion on Cu as well as OSG intermetal dielectric (IMD), though the /spl alpha/-SiC film has a very slow deposition rate. We believe that the /spl alpha/-SiCN//spl alpha/-SiC bilayer dielectric is a favorable combination for the ESL because /spl alpha/-SiCN can protect /spl alpha/-SiC from plasma attack during the photoresist stripping.