Highly Stable Ultrathin Carbosiloxane Films by Molecular Layer

Sep 20, 2013 - Carbosiloxane thin films are grown by molecular layer deposition (MLD) using 1,2-bis[(dimethylamino)dimethylsilyl]ethane and ozone ...
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Highly Stable Ultrathin Carbosiloxane Films by Molecular Layer Deposition Han Zhou and Stacey F. Bent* Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States ABSTRACT: Carbosiloxane thin films are grown by molecular layer deposition (MLD) using 1,2-bis[(dimethylamino)dimethylsilyl]ethane and ozone precursors. The films exhibit a constant growth rate per MLD cycle and saturation behavior in exposure times for both reactants. Fourier-transform infrared spectroscopic study reveals characteristic carbosiloxane vibrational absorptions. The deposition of carbosiloxane films is further confirmed by X-ray photoelectron spectroscopy, and the film composition is shown to be dependent on ozone exposure time. The carbosiloxane films exhibit excellent stability when treated with acid, base, and organic solvent. Thermal stability studies demonstrate that the films are stable to 400 °C, with little thickness loss even at 600 °C, which is comparable to carbosiloxane films deposited by other techniques.

1. INTRODUCTION The tremendous advances made in modern integrated circuits have greatly benefitted from the ongoing development of new materials. For example, as the sizes of individual devices continue to be scaled in order to increase device densities and performance, new materials have been developed for back-endof-line (BEOL) processes. SiO2 has been largely replaced by low dielectric constant (low-κ) materials to reduce the capacitance of the BEOL dielectric layer.1 Carbon-doped silica, also known as carbon-doped oxide (CDO), organosilicate, silicon oxycarbide, or carbosiloxane, comprises an important class of low-κ materials.2−4 By introducing organic constituents with a lower dielectric constant, e.g. CHx groups, into a SiO2 matrix, the SiO2 network can be broken up, further reducing the κ value. Additional reductions in dielectric constant are achieved by incorporating nanometer-scale pores into the low-κ material.5 However, the pores introduce new problems to the integration of porous low-κ materials, since they may render the dielectric layer vulnerable to the penetration of moisture as well as of metal precursors used in subsequent processing steps, e.g., atomic layer deposition (ALD) of a barrier layer.3 Such penetration can result in a higher κ value and a lower breakdown voltage of the dielectric layer. To overcome this challenge, new processes and materials including plasma treatment,6−8 surface chemical modification,9−11 and deposition of thin filmshave been developed to seal the pores and protect the low-κ dielectrics. Plasma treatment can form a densified surface layer to provide a sealing effect, but it has been shown to lack effectiveness in sealing the side-walls of pores with high aspect ratio.8 Self-assembled monolayers (SAMs), which are typically formed by reaction between silane reagents and surface hydroxyl groups of the pores, have been studied as pore-sealing materials as well.10,11 Although there are observations showing that the SAMs have a repairing effect on damaged pores, it is unclear whether monolayer coverage can provide sufficient sealing, especially © 2013 American Chemical Society

when the SAM formation is performed in solution phase where conformal coating can be challenging. On the other hand, thin films deposited from the vapor phase, for example, via atomic layer deposition (ALD), may provide a highly conformal sealing layer with a high degree of control over film thickness. Nanometer-scale SiO2 films have been deposited by catalyzed ALD12 and plasma-assisted ALD13 with excellent conformal coverage over the pores. In this case, though, the SiO2 coating may undesirably increase the dielectric constant of the low-κ material. Silicon oxycarbide (SiOxCy) and silicon hydrocarbide (SiCH) films, which have the advantage of possessing similar composition and dielectric constants as low-κ materials, have been deposited by chemical vapor deposition (CVD) as poresealing films;14,15 however, the CVD technique can lack full control over film thickness and may completely fill the pores when the pore sizes are only a few nanometers.16 Hence, it is desirable to develop new processes for depositing low-κ-like thin films that provide a high degree of control over thickness and excellent conformality. In addition to applications as poresealing materials for low-κ dielectrics, carbosiloxane films have also been applied as separation membranes with molecular sieving functions,17,18 in which a high level of control over the film properties is also desirable. Molecular layer deposition (MLD) is an analogue to ALD that can provide excellent control over film thickness and composition.19,20 In addition, highly conformal coatings over features with high-aspect-ratio have been achieved by MLD.21,22 A variety of organic polymeric films21,23−28 as well as inorganic−organic hybrid materials29−34 have been deposited using MLD. The inorganic−organic hybrid MLD films have been found to have lower film density and higher porosity compared to their purely inorganic counterparts.29,35 These Received: June 14, 2013 Revised: September 1, 2013 Published: September 20, 2013 19967

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Figure 1. MLD scheme for depositing carbosiloxane films: (a) idealized process with only Si−N bond cleavage and (b) more realistic process with Si−C and Si−N bond cleavage.

rate and saturation behavior studies were as follows: 300 s DDSE dose, 120 s nitrogen purge, 10 s O3 dose, and 30 s nitrogen purge. Films were deposited on Si(100) wafers with a 4 nm thick thermal oxide unless specified otherwise. Prior to MLD, the silicon wafers were cleaned with piranha solution. The samples were removed from the reactor after MLD for ex situ characterization. A J.A. Woollam alpha-SE laser spectroscopic ellipsometer was used for ellipsometry measurements, and data were fitted using a Cauchy model. FTIR spectra were collected with a Thermo Nicolet 6700 FTIR spectrometer in the transmission mode using a MCT-A detector. The spectrum was taken with 200 scans at a resolution of 4 cm−1. Piranha-cleaned silicon samples were used as a background reference for FTIR measurements. XPS measurements were performed on a Physical Electronics, Inc. 5000 Versaprobe spectrometer using an excitation source of Al Kα radiation (1486.6 eV). Survey scans and high-resolution (HR) scans were performed using an energy step of 1 and 0.1 eV, respectively. Film morphology was measured on a Park XE-70 atomic force microscope (AFM) using a silicon nitride tip in a tapping mode. For chemical stability tests, 37% hydrochloric aqueous solution and 25 wt % tetramethylammonium hydroxide (TMAH) aqueous solution were purchased from Sigma-Aldrich and diluted in water to 0.2 M. A vacuum tube furnace was used for annealing the carbosiloxane films, with a nitrogen flow at 5 sccm.

advantages make the MLD technique a potential candidate for depositing pore-sealing materials. However, to date, the development of inorganic−organic hybrid MLD systems has been focused on metal-based materials, such as aluminum alkoxide31,32 and zinc alkoxide,33,34 which may not provide sufficiently low dielectric constants due to the presence of Al− O and Zn−O moieties. In this study, we introduce a process for depositing carbosiloxane thin films by MLD using 1,2-bis[(dimethylamino)dimethylsilyl]ethane (DDSE) and ozone (O3). These films demonstrate characteristic MLD growth behavior, such as a constant growth rate and saturated growth for both reactants. Fourier transform infrared (FTIR) spectra of the MLD carbosiloxane films agree well with films deposited by CVD. X-ray photoelectron spectroscopy (XPS) confirms the formation of carbosiloxane films. In addition, the carbosiloxane MLD films have excellent chemical and thermal stability, which are important properties for the application of pore-sealing materials.

2. EXPERIMENTAL METHODS A custom-made reactor controlled by LabVIEW software was used for deposition of the carbosiloxane films. A showerhead precursor inlet and vacuum pumping lines were connected to the top and bottom of the chamber, respectively. The substrates were placed on a 4 in. diameter substrate heater. The 1,2bis[(dimethylamino)dimethylsilyl]ethane (DDSE, 96% from Sigma-Aldrich) precursor was contained in a stainless steel bubbler. The bubbler temperature was kept at 35 °C to obtain sufficient vapor pressure. The counter reactant, O3, was generated in situ during the MLD process by an O3 generator (IN USA OG 5000 Series) with pure O2 supplied from a 99.99% O2 cylinder. O3 concentration was set to 21%. N2 was used for both the O3 carrier gas and the purging gas, with flow rates controlled by a mass flow controller fixed at 30 sccm for both purposes. The substrate temperature was 110 °C, and the reactor was maintained at 100 °C during the deposition. Further information on the reactor configuration can be found elsewhere.36 A complete MLD cycle consisted of a sequence of the following steps: DDSE dose, nitrogen purge, O3 dose, nitrogen purge. During DDSE doses, the pump was isolated to allow for greater DDSE pressures in the reactor, and the reactor was backfilled with DDSE by opening the valve to the DDSE bubbler for 30 s; this quantity of precursor was then held for the rest of the dose time. The nominal dose times for growth

3. RESULTS AND DISCUSSION The idealized MLD reaction between DDSE and O3 is illustrated in Figure 1a, showing O3 reacting with NMe2 groups, which are the most reactive groups in the DDSE precursor. Under this ideal situation, linear carbosiloxane polymer chains are expected. However, the highly reactive O3 can also break some Si−C bonds and consequently form a cross-linked carbosiloxane network, as shown in Figure 1b. A constant growth rate (thickness linear with cycle number) is an important characteristic of MLD. To test the growth behavior of the carbosiloxane MLD process, film thicknesses were measured by ellipsometry after different numbers of MLD cycles, as shown in Figure 2a. It can be seen that the film thickness increases proportionally to the number of MLD cycles, with a slope yielding a growth rate of 0.2 Å/cycle. This growth rate, while close to the 0.3 Å/cycle growth rate reported by Jiang et al.13 for plasma-assisted ALD of SiO2 using tetraethyl orthosilicate and oxygen precursors, is much less than 19968

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hydroxyl groups formed at the film surface by previous O3 exposure. It can be seen from Figure 2c that saturation of the growth rate is reached within 20 s of O3 exposure. Although the trend may not be significant, there also appears to be a small drop-off observed at the longest ozone exposures, suggesting that the O3 exposure time may impose a competition between creation of active growth sites and cleavage of the chains: namely, with a shorter O3 exposure, an insufficient number of Si−OH groups are generated, resulting in a smaller concentration of active surface sites to react with the subsequently dosed DDSE precursor; in contrast, with a longer O3 exposure (e.g., 30 s), although more active sites are generated, more Si−C bonds are also broken and converted into Si−OH groups, resulting in deposition of a SiO2-like film, which has a shorter unit length. Further studies should be performed to characterize the mechanistic effect of O3 exposure time in more detail. To investigate the chemical bonding within the deposited film, an FTIR spectrum of a 15 nm thick carbosiloxane MLD film grown with 300 s DDSE and 20 s O3 exposures is shown in Figure 3a. Features common to carbosiloxane films are evident. A SiO−H stretching mode is found at 3661 cm−1,3,37 with the hydroxyl incorporation resulting from the reaction between O3 and the deposited carbosiloxane film. C−H stretches assigned to CH3 and CH2 groups are present in the 2800−3000 cm−1 region, with ν(CH3) and ν(CH2) appearing at 2968 and 2917 cm−1, respectively,37 confirming that some Si−CH3 and Si− CH2 moieties remain intact after the MLD reaction with O3. The next band encountered is in the region between 1245 and 1300 cm−1, assigned to an Si−CH3 bending deformation, δ(Si− CH3). Burkey et al. have found that a high silicon oxidation state can blue-shift the δ(Si−CH3) peak.38 A deconvolution of this peak is shown in the inset to Figure 3a. It can be seen that two peaks are present: a major peak at 1277 cm−1 and a shoulder at 1263 cm−1, attributed to the O3Si(CH3) group and O2Si(CH3)2 group, respectively. This observation suggests that, similar to carbosiloxane films deposited by plasma enhanced CVD (PECVD) using trimethylsilane and O3,39 multiple silicon oxidation states may exist in the films grown by MLD. Moreover, the presence of the characteristic O3Si(CH3) and O2Si(CH3)2 carbosiloxane absorptions suggests that the MLD reaction proceeds with Si−C bond cleavage to various degrees in addition to breaking Si−N bonds of the DDSE precursor. The strongest peak in Figure 3a is the Si−O−Si band in the region between 1250 and 950 cm−1. This broad absorption band indicates the coexistence of several different Si−O−Si bonding environments due to various configurations.37 The last two features observed in the FTIR spectrum are peaks at 840 and 802 cm−1, which can be assigned to Si−C stretching vibrations of Si(CH3)3 and Si(CH3)2 moieties, respectively.37 The chemical composition of the carbosiloxane MLD film was obtained by X-ray photoelectron spectroscopy. Only C, Si, and O signals are observed in the XPS spectrum of a 15 nm carbosiloxane film deposited on a SiO2/Si substrate using 20 s O3 exposure, as shown in Figure 3b. A thick film was grown for this experiment to mitigate the contribution from the underlying Si substrate. The absence of any N signal confirms complete removal of NMe2 groups in the DDSE precursor by reaction with O3. The atomic concentration of C, Si, and O is 16.6 ± 0.4%, 27.6 ± 0.2%, and 55.8 ± 0.6%, respectively. Compared to carbosiloxane films deposited using other techniques, the carbon concentration of the MLD film is within the typical range of 10−30%;4 it is also higher than that

Figure 2. (a) MLD film thickness as a function of number of cycles, with error bars showing the standard deviation measured across multiple samples in the same MLD batch, and saturation curves showing the dependence of film thickness (after 100 cycles) on (b) DDSE exposure time and (c) O3 exposure time.

the unit chain length expected for the idealized reaction scheme of Figure 1a in which only the NMe2 groups react with O3. This low growth rate therefore suggests that a significant fraction of Si−C moieties also react with O3, by which the Si−C bonds are cleaved and new Si−O bonds are formed, resulting in films with more SiO2-like structures. Interestingly, the best data fitting was obtained with a nonzero y-intercept, leading to an extrapolated film thickness of 4.4 Å. This suggests a fast initial growth, which is in good agreement with the film thickness of 4.5 Å measured after only one DDSE dose in a separate experiment, followed by much slower growth. This initial film growth can be explained by the formation of a carbosiloxane monolayer via the reaction between DDSE and the hydroxyl groups on the SiO2 surface. Although this might suggest using H2O as the counterreactant for the MLD process, tests of subsequent film deposition using water instead of O3 did not achieve a continuous film growth. This is likely due to the “dual reaction” of the NMe2 groups on both ends of the precursor, which significantly reduces surface reactive sites and terminates film growth. Using O3 as the counter-reactant, in contrast, can continuously generate new surface hydroxyl groups to ensure a sustained film growth. To further test the mechanistic differences between use of O3 and H2O as the counterreactant, additional studies employing in situ techniques to exclude complications caused by ambient oxygen should be carried out. In addition to a constant growth rate, saturation behavior for both precursors is expected for a MLD process, since the MLD films are deposited by self-limiting surface reactions.20 A series of carbosiloxane MLD experiments were performed with the exposure time of one precursor as the only variant and all other deposition parameters unchanged. For each MLD run, film thicknesses were measured after 100 cycles and plotted against the precursor exposure time, as shown in Figures 2b,c. As seen in Figure 2b, saturated film growth was observed after a relatively long DDSE exposure time of about 120 s, likely due to the reaction time required for NMe2 groups to react with 19969

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signal provides strong evidence for the growth of a carbosiloxane film. To further explore the effect of O3 exposure time on film growth, a series of ultrathin carbosiloxane films were deposited on Al2O3-coated substrates for 100 MLD cycles using different O3 exposure lengths. Using 20 s O3 exposure, the C/Si atomic ratio is determined to be 0.87 by XPS measurement. We note that this is higher than the value of 0.60 measured for the 15 nm film grown directly on the SiO2/Si substrate, possibly because the latter film underwent a much longer cumulative O3 exposure time over the large number of MLD cycles required to grow the thick film, which can increase the degree of Si−C bond cleavage and in turn decrease the C/Si ratio. The C/Si atomic ratios in MLD films grown on Al2O3 with O3 exposure times of 10 and 30 s are 1.02 and 0.74, respectively. This observation shows that O3 exposure time plays an important role in film composition, with shorter exposure times leading to less Si−C bond cleavage and more carbon-rich films, as inferred from the saturation curve data of Figure 2c. More detailed investigation of the effect of O3 exposure time on film composition and properties should be performed in the future. In addition to the vibrational frequency of the Si−CH3 band in the FTIR spectrum, the binding energy of the Si(2p) core level peak in the XPS spectrum is also a good indicator of the chemical oxidation state of Si in the carbosiloxane film.42,43 High-resolution XPS scans of Si(2p) were performed, and the results are shown in Figure 3c. Right after piranha cleaning, the bare SiO2/Si substrate showed two distinct peaks: a Si peak at a lower binding energy of 99.3 eV and a SiO2 peak at a higher binding energy of 103.5 eV. For a very thin (3 nm) carbosiloxane MLD film deposited on a SiO2/Si substrate, the emergence of a third peak with a binding energy of 102.8 eV is attributed to SiOxCy in the carbosiloxane film, since Si in the carbosiloxane film is expected to have an oxidation state higher than Si but lower than SiO2. Si and SiO2 peaks are still present in this spectrum because the carbosiloxane film is not thick enough to block the signals from the underlying substrate. As the carbosiloxane film thickness increases to 15 nm, only the SiOxCy peak is present while the Si and SiO2 peaks are no longer observed, as shown in Figure 3c. Moreover, for an ultrathin (4 nm) film deposited on an Al2O3-coated substrate, the SiOxCy peak is the only evident peak, since the signals from the underlying substrate are blocked by the Al2O3 coating. According to Alexander et al.,43 the binding energy of 102.8 eV for the SiOxCy peak suggests that the carbosiloxane MLD film is mainly composed of O3Si(CH3) moieties, which agrees with the results of the FTIR spectroscopic investigation. An advantage of MLD as a deposition method is that the MLD films often have smooth morphologies. An AFM measurement (not shown) taken on an area of 156 μm2 of an 18 nm thick carboxiloxane MLD film shows that the RMS roughness is 0.77 nm, about only 4.3% of the film thickness. The RMS roughness of the carbosiloxane MLD film is higher than that of a pure organic polyurea MLD film (0.10 nm),28 while close to that of a carbosiloxane film deposited by PECVD (0.72 nm).44 For MLD thin films to be integrated into semiconductor fabrication, the films must have good chemical and thermal stability in order to withstand various downstream processing steps; for example, processing temperatures as high as 425 °C may be frequently used.2 To test the chemical stability of the carbosiloxane MLD films, three different treatments were performed on films with thicknesses of about 19 nm, including

Figure 3. (a) FTIR spectrum of a 15 nm carbosiloxane MLD film with the inset showing peak fitting for the δ(C−H) peak. (b) XPS survey scan spectra of carbosiloxane MLD films (c) XPS high-resolution scans of the Si(2p) peaks.

of films grown by inductively coupled plasma CVD (ICPCVD) using bistrimethylsilylmethane and oxygen40 but lower than those made by PECVD using trimethylsilane and CO2.41 To conclusively exclude the possibility of the underlying SiO2/Si substrate contributing to the total apparent Si signal, the MLD carbosiloxane films were also deposited on substrates precoated with 18 nm Al2O3 films grown by ALD. Figure 3b illustrates an XPS spectrum of a 4 nm carbosiloxane MLD film deposited on an Al2O3-coated substrate. Since the XPS signal generated by the SiO2/Si substrate is shielded by the relatively thick Al2O3 layer between the carbosiloxane MLD film and the substrate (as confirmed by the absence of any Si signal in XPS spectra taken of Al2O3-coated substrates prior to MLD), the presence of Si 19970

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thermal stability of the MLD carbosiloxane films are comparable to those deposited by other techniques. For example, films made by a sol−gel process had 3% and 20% film loss upon 150 and 600 °C annealing, respectively.45 PECVD carbosiloxane films also showed similar thermal stability.46 Thus, it is evident that the carbosiloxane films deposited by MLD exhibit excellent thermal stability in addition to high chemical stability, demonstrating the robustness of the MLD films.

a strong base treatment using 0.2 M aqueous TMAH, a strong acid treatment using 0.2 M aqueous HCl, and an organic solvent treatment using acetone. Carbosiloxane films were immersed in the three solutions for 2 min followed by rinsing with deionized water. Figure 4a shows the thickness and

4. CONCLUSIONS We have introduced a new strategy for depositing carbosiloxane thin films by MLD using DDSE and O3 precursors. A constant film growth rate and saturation behavior in exposure times of both DDSE and O3 are observed for the MLD films. The films exhibit characteristic vibrational modes expected for carbosiloxane films as shown by FTIR spectroscopy. XPS measurements confirm the deposition of carbosiloxane films and show a typical carbon concentration for the carbosiloxane films. O3 exposure time is seen to have a strong effect on film composition. Short O3 exposure times leads to more carbonrich films, while long O3 exposure times result in deposition of more SiO2-like films. Moreover, the vibrational frequency of Si−CH3 groups together with the binding energy of the Si(2p) peak suggest that the silicon atoms in the film are mostly coordinated with three oxygen atoms as O3Si(CH3) moieties. AFM studies show that smooth film morphology can be obtained. The MLD carbosiloxane films exhibit excellent chemical stability. Acid, base, and organic solvent treatments have a negligible effect on film thickness and composition. The films are also thermally stable, with only 13% shrinkage in film thickness upon 600 °C annealing.

Figure 4. (a) Carbosiloxane MLD film thicknesses (blue circles) and compositions after different chemical treatments. (b) Carbosiloxane MLD film thickness changes (blue circles) and resulting compositions after 20 min vacuum annealing at the stated temperatures.

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected] (S.F.B.).

composition changes after the chemical treatments. As can be seen, negligible changes were observed in both film thickness and composition, indicating excellent chemical stability of the carbosiloxane films. Chemical treatments may affect the roughness of the MLD films. However, our studies show that the effect is small. For example, after the acid treatment, a 19 nm thick film had a RMS roughness of 1.06 nm, about 5.6% of the film thickness, which is slightly higher than the roughness of 4.3% for the as-deposited film. It should be noted that purely organic polyurea MLD films also showed good chemical stability in acid and base solutions.28 However, they often do not have good thermal stability. For example, polythiourea MLD films were completely desorbed or decomposed under 250 °C vacuum anneal.21 In contrast, the carbosiloxane MLD films show greatly enhanced thermal stability as evaluated by a series of vacuum annealing experiments represented in Figure 4b. After annealing at 300 °C, no film thickness loss was observed, and a slight decrease in carbon concentration occurred, likely due to a small loss of carbon-containing moieties. 400 °C annealing resulted in a small thickness loss of about 6%, while the film composition was very close to that of the film annealed at 300 °C. Further annealing up to 600 °C resulted in only 13% thickness loss with negligible change in film composition. We note that no significant change in optical properties of the films was observed after annealing to 600 °C, supporting the assignment of the ellipsometric differences to a change in film thickness rather than to film densification. The

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. Han-Bo-Ram Lee and Dr. Scott Geyer for help with the deposition reactor and Artit Wangperawong for help with vacuum annealing experiment. S.F.B. acknowledges support from the National Science Foundation (CHE 1213879). Financial support from the SRC MSR program is also acknowledged.

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REFERENCES

(1) List, S.; Bamal, M.; Stucchi, M.; Maex, K. A Global View of Interconnects. Microelectron. Eng. 2006, 83 (11−12), 2200−2207. (2) Morgen, M.; Ryan, E. T.; Zhao, J. H.; Hu, C.; Cho, T. H.; Ho, P. S. Low Dielectric Constant Materials for ULSI Interconnects. Annu. Rev. Mater. Sci. 2000, 30, 645−680. (3) Maex, K.; Baklanov, M. R.; Shamiryan, D.; Iacopi, F.; Brongersma, S. H.; Yanovitskaya, Z. S. Low Dielectric Constant Materials for Microelectronics. J. Appl. Phys. 2003, 93 (11), 8793− 8841. (4) Reinhardt, K. A.; Reidy, R. F.; Daviot, J. Handbook of Cleaning for Semiconductor Manufacturing - Fundamentals and Applications; Reinhardt, K. A., Reidy, R. F., Eds.; Wiley-Scrivener: 2011. (5) Grill, A. Porous PSiCOH Ultralow-k Dielectrics for Chip Interconnects Prepared by PECVD. Annu. Rev. Mater. Res. 2009, 39, 49−69. 19971

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Article

(25) Kim, A.; Filler, M. A.; Kim, S.; Bent, S. F. Layer-by-Layer Growth on Ge(100) Via Spontaneous Urea Coupling Reactions. J. Am. Chem. Soc. 2005, 127 (16), 6123−6132. (26) Loscutoff, P. W.; Zhou, H.; Clendenning, S. B.; Bent, S. F. Formation of Organic Nanoscale Laminates and Blends by Molecular Layer Deposition. ACS Nano 2010, 4 (1), 331−341. (27) Yoshimura, T.; Tatsuura, S.; Sotoyama, W. Polymer-Films Formed with Monolayer Growth Steps by Molecular Layer Deposition. Appl. Phys. Lett. 1991, 59 (4), 482−484. (28) Zhou, H.; Bent, S. F. Molecular Layer Deposition of Functional Thin Films for Advanced Lithographic Patterning. ACS Appl. Mater. Interfaces 2011, 3 (2), 505−511. (29) Abdulagatov, A. I.; Hall, R. A.; Sutherland, J. L.; Lee, B. H.; Cavanagh, A. S.; George, S. M. Molecular Layer Deposition of Titanicone Films Using TiCl4 and Ethylene Glycol or Glycerol: Growth and Properties. Chem. Mater. 2012, 24 (15), 2854−2863. (30) George, S. M.; Lee, B. H.; Yoon, B.; Abdulagatov, A. I.; Hall, R. A. Metalcones: Hybrid Organic-Inorganic Films Fabricated Using Atomic and Molecular Layer Deposition Techniques. J. Nanosci. Nanotechnol. 2011, 11 (9), 7948−7955. (31) Lee, B. H.; Yoon, B.; Anderson, V. R.; George, S. M. Alucone Alloys with Tunable Properties Using Alucone Molecular Layer Deposition and Al2O3 Atomic Layer Deposition. J. Phys. Chem. C 2012, 116 (5), 3250−3257. (32) Lee, Y.; Yoon, B.; Cavanagh, A. S.; George, S. M. Molecular Layer Deposition of Aluminum Alkoxide Polymer Films Using Trimethylaluminum and Glycidol. Langmuir 2011, 27 (24), 15155− 15164. (33) Peng, Q.; Gong, B.; VanGundy, R. M.; Parsons, G. N. “Zincone” Zinc Oxide-Organic Hybrid Polymer Thin Films Formed by Molecular Layer Deposition. Chem. Mater. 2009, 21 (5), 820−830. (34) Yoon, B.; O’Patchen, J. L.; Seghete, D.; Cavanagh, A. S.; George, S. M. Molecular Layer Deposition of Hybrid Organic-Inorganic Polymer Films Using Diethylzinc and Ethylene Glycol. Chem. Vap. Deposition 2009, 15 (4−6), 112−121. (35) Qin, Y.; Yang, Y.; Scholz, R.; Pippel, E.; Lu, X. L.; Knez, M. Unexpected Oxidation Behavior of Cu Nanoparticles Embedded in Porous Alumina Films Produced by Molecular Layer Deposition. Nano Lett. 2011, 11 (6), 2503−2509. (36) Lee, H. B. R.; Bent, S. F. Microstructure-Dependent Nucleation in Atomic Layer Deposition of Pt on TiO2. Chem. Mater. 2012, 24 (2), 279−286. (37) Grill, A.; Neumayer, D. A. Structure of Low Dielectric Constant to Extreme Low Dielectric Constant SiCOH Films: Fourier Transform Infrared Spectroscopy Characterization. J. Appl. Phys. 2003, 94 (10), 6697−6707. (38) Burkey, D. D.; Gleason, K. K. Organosilicon Thin Films Deposited from Cyclic and Acyclic Precursors Using Water as an Oxidant. J. Electrochem. Soc. 2004, 151 (5), F105−F112. (39) Das, G.; Mariotto, G.; Quaranta, A. Microstructural Evolution of Thermally Treated Low-Dielectric Constant SiOC: H Films Prepared by PECVD. J. Electrochem. Soc. 2006, 153 (3), F46−F51. (40) Yang, C. S.; Yu, Y. H.; Lee, K. M.; Lee, H. J.; Choi, C. K. The Influence of Carbon Content in Carbon-Doped Silicon Oxide Film by Thermal Treatment. Thin Solid Films 2003, 435 (1−2), 165−169. (41) Chiang, C. C.; Ko, I. H.; Chen, M. C.; Wu, Z. C.; Lu, Y. C.; Jang, S. M.; Liang, M. S. Physical and Barrier Properties of PECVD Amorphous Silicon-Oxycarbide from Trimethylsilane and CO2. J. Electrochem. Soc. 2004, 151 (10), G704−G708. (42) NIST X-Ray Photoelectron Spectroscopy Database, Version 4.1; National Institute of Standards and Technology, Gaithersburg, 2012. (43) Alexander, M. R.; Short, R. D.; Jones, F. R.; Michaeli, W.; Blomfield, C. J. A Study of HMDSO/O2 Plasma Deposits Using a High-Sensitivity and -Energy Resolution XPS Instrument: Curve Fitting of the Si 2p Core Level. Appl. Surf. Sci. 1999, 137, 179−183. (44) Borst, C. L.; Korthuis, V.; Shinn, G. B.; Luttmer, J. D.; Gutmann, R. J.; Gill, W. N. Chemical-Mechanical Polishing of SiOC Organosilicate Glasses: The Effect of Film Carbon Content. Thin Solid Films 2001, 385 (1−2), 281−292.

(6) Cui, H.; Carter, R. J.; Moore, D. L.; Peng, H. G.; Gidley, D. W.; Burke, P. A. Impact of Reductive N2/H2 Plasma on Porous LowDielectric Constant SiCOH Thin Films. J. Appl. Phys. 2005, 97 (11), 113302. (7) Peng, H. G.; Chi, D. Z.; Wang, W. D.; Li, J. H.; Zeng, K. Y.; Vallery, R. S.; Frieze, W. E.; Skalsey, M. A.; Gidley, D. W.; Yee, A. F. Pore Sealing by NH3 Plasma Treatment of Porous Low Dielectric Constant Films. J. Electrochem. Soc. 2007, 154 (4), G85−G94. (8) Shoeb, J.; Kushner, M. J. Mechanisms for Sealing of Porous Lowk SiOCH by Combined He and NH3 Plasma Treatment. J. Vac. Sci. Technol., A 2011, 29 (5), 051305. (9) Xie, B.; Choate, L.; Muscat, A. J. Repair and Capping of Porous MSQ Films Using Chlorosilanes and Supercritical CO2. Microelectron. Eng. 2005, 80, 349−352. (10) Liu, J.; Kim, W.; Bao, J.; Shi, H.; Baek, W.; Ho, P. S. Restoration and Pore Sealing of Plasma Damaged Porous Organosilicate Low K Dielectrics with Phenyl Containing Agents. J. Vac. Sci. Technol., B 2007, 25 (3), 906−912. (11) Armini, S.; Prado, J. L.; Swerts, J.; Sun, Y.; Krishtab, M.; Meersschaut, J.; Blauw, M.; Baklanov, M.; Verdonck, P. Pore Sealing of Porous Ultralow-k Dielectrics by Self-Assembled Monolayers Combined with Atomic Layer Deposition. ECS Solid State Lett. 2012, 1 (2), P42−P44. (12) de Rouffignac, P.; Li, Z. W.; Gordon, R. G. Sealing Porous Lowk Dielectrics with Silica. Electrochem. Solid-State Lett. 2004, 7 (12), G306−G308. (13) Jiang, Y. B.; Liu, N. G.; Gerung, H.; Cecchi, J. L.; Brinker, C. J. Nanometer-Thick Conformal Pore Sealing of Self-Assembled Mesoporous Silica by Plasma-Assisted Atomic Layer Deposition. J. Am. Chem. Soc. 2006, 128 (34), 11018−11019. (14) Whelan, C. M.; Le, Q. T.; Cecchet, F.; Satta, A.; Pireaux, J. J.; Rudolf, P.; Maex, K. Sealing of Porous Low-k Dielectrics Ellipsometric Porosimetry Study of UV-O3 Oxidized SiOxCy Films. Electrochem. Solid-State Lett. 2004, 7 (2), F8−F10. (15) Furuya, A.; Yoneda, K.; Soda, E.; Yoshie, T.; Okamura, H.; Shimada, M.; Ohtsuka, N.; Ogawa, S. Ultrathin Pore-Seal Film by Plasma Enhanced Chemical Vapor Deposition SiCH from Tetramethylsilane. J. Vac. Sci. Technol., B 2005, 23 (6), 2522−2525. (16) Baklanov, M. R.; Kondoh, E.; Lin, E. K.; Gidley, D. W.; Lee, H. J.; Mogilnikov, K. P.; Sun, J. P. Comparative Study of Porous SOG Films with Different Non-Destructive Instrumentation. Proc. IEEE 2001 Int. Interconnect Technol. Conf. 2001, 189−191. (17) Castricum, H. L.; Sah, A.; Kreiter, R.; Blank, D. H. A.; Vente, J. F.; ten Elshof, J. E. Hybrid Ceramic Nanosieves: Stabilizing Nanopores with Organic Links. Chem. Commun. 2008, 0 (9), 1103−1105. (18) Castricum, H. L.; Sah, A.; Kreiter, R.; Blank, D. H. A.; Vente, J. F.; ten Elshof, J. E. Hydrothermally Stable Molecular Separation Membranes from Organically Linked Silica. J. Mater. Chem. 2008, 18 (18), 2150−2158. (19) Ritala, M.; Leskela, M. Atomic Layer Deposition. In Handbook of Thin Film Materials; Nalwa, H. S., Ed.; Academic Press: San Diego, CA, 2002; Vol. 1. (20) George, S. M.; Yoon, B.; Dameron, A. A. Surface Chemistry for Molecular Layer Deposition of Organic and Hybrid Organic-Inorganic Polymers. Acc. Chem. Res. 2009, 42 (4), 498−508. (21) Loscutoff, P. W.; Lee, H.-B.-R.; Bent, S. F. Deposition of Ultrathin Polythiourea Films by Molecular Layer Deposition. Chem. Mater. 2010, 22 (19), 5563−5569. (22) Gong, B.; Peng, Q.; Parsons, G. N. Conformal Organic Inorganic Hybrid Network Polymer Thin Films by Molecular Layer Deposition Using Trimethylaluminum and Glycidol. J. Phys. Chem. B 2011, 115 (19), 5930−5938. (23) Adarnczyk, N. M.; Dameron, A. A.; George, S. M. Molecular Layer Deposition of Poly(p-Phenylene Terephthalamide) Films Using Terephthaloyl Chloride and p-Phenylenediamine. Langmuir 2008, 24 (5), 2081−2089. (24) Du, Y.; George, S. M. Molecular Layer Deposition of Nylon 66 Films Examined Using in Situ FTIR Spectroscopy. J. Phys. Chem. C 2007, 111 (24), 8509−8517. 19972

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The Journal of Physical Chemistry C

Article

(45) Rathore, J. S.; Interrante, L. V.; Dubois, G. Ultra Low-K Films Derived from Hyperbranched Polycarbosilanes (HBPCS). Adv. Funct. Mater. 2008, 18 (24), 4022−4028. (46) Chiang, C. C.; Chen, C. C.; Li, L. J.; Wu, Z. C.; Jang, S. M.; Liang, M. S. Physical and Barrier Properties of Amorphous SiliconOxycarbide Deposited by PECVD from Octamethylcyclotetrasiloxane. J. Electrochem. Soc. 2004, 151 (9), G612−G617.

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