Low-k dielectric material removal rate, which is significantly affected by process factors such as polishing load, wafer carrier rotation, platen rotation speed and pad age, is one of the critical issues in CMP planarization of a dielectric film when concerning productivity, throughputs and stabilization of the process, especially when trying to achieve a target polishing thickness. Scratching is another critical issue in low-k dielectric filmi CMP planarization due to the lower hardness relative to silicon dioxide. This research relates to a methodology for in-situ monitoring of the low-k dielectric material CMP planarization process, specifically for monitoring material removal rate and scratch occurrence, using acoustic emission (AE) sensing technology.

Systematic investigations of CMP process variables on AE signals were carried out in this research. The sensitivity of AE to polishing load, polishing speed, wafer surface roughness (wafer pattern density) and pad roughness were verified. The results showed that, under steady state, the AE rms signal increases with increasing polishing load, polishing speed, slurry particle size, wafer surface roughness and pad roughness.

Based on the research in tribology and other application fields of loose abrasive machining such as lapping and polishing, scratching was known to be caused by the presence of particles which are much larger than average slurry particles. It has been proven that scratching can be avoided or reduced by timely cleaning the slurry supply system. Therefore, to avoid scratching, one strategy is to develop an in-situ method for detecting larger particles involved in CMP process. In this paper, the high sensitivity of AE signals to the presence of larger particles during CMP was experimentally verified.

The quality of benzocyclobutene (BCB) and Parylene-N (PA-N) films after chemical-mechanical polishing (CMP) is influenced by 3 factors: slurry composition, quality of the as-deposited film or post-deposition treated film, and polishing time. The quality of the films has been investigated by using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). It is shown that the higher the quality of the as-deposited film (or post-deposition treated film), the higher the quality of the polished film. The polishing time has little effect on the surface characteristics of high quality PA-N films, however it has an effect on BCB film. This is attributed to the structure and thermal-stability and higher chemical resistance of PA-N. The RMS surface roughness measured by AFM, for as-deposited PA-N is 90Å. The roughness after CMP processes is greater than 200Å. The roughness for as-spin-coated and polished BCB film is 5A, and 20Å, respectively. The morphology of the PA-N film, either as-deposited or polished, is not as good as the BCB film. A slurry which is good for BCB polishing is not good for PA-N polishing, and vice versa. These results indicate that the nature of the polymer film, including its chemical structure as well as the quality of the as-deposited/post-deposition treated film, plays an important role in polymer CMP.

Using Si and GaAs substrates, the coefficient of thermal expansion (CTE) and the bi-axial modulus of thin hydrogen silsesquioxanes (HSQ) films are deduced by means of wafer curvature measurement. The same properties of plasma-enhanced CVD oxide are also reported.

The wide variety of low-k dielectric materials and processes for ULSI interconnection were sorted to create generic process flows. Average material and equipment costs were then used as inputs to a generic cost-per-wafer (CPW) model for dielectric deposition (not including the costs of dielectric CMP, metallization, or lithography). The model outputs are internally consistent, and useful for comparison of similar processes.

Plasma deposited fluoropolymer films are shown to have composition, chemical structures and properties variable continuously in a very broad range. Films obtained under high fragmentation and structure retention conditions are discussed and compared. The mechanism of deposition is shown to explain etching-deposition competition. Finally, actinometric spectroscopy is discussed briefly as a semi-quantitative diagnostics tool enabling the control of the chemistry of the process under high fragmentation conditions‥

Improvements in the properties of Parylene may enable their use in high performance integrated circuits. Parylenes are a class of polymers formed by chemical vapor deposition which nearly meet the high standards of the low-k triumvirate, namely, 1) adhesion, particularly to SiO2, 2) thermal stability above 400 Celsius, and 3) permittivity less than 2.7. Parylene-N has been incorporated into both aluminum-1 and copper-2 based metallization schemes, however, improvements in the adhesion and thermal stability are still needed to simplify and increase the robustness of the integration schemes. Additionally, a reduction in the permittivity would be beneficial from both device performance and extendibility points-of-view. We have synthesized various Parylene-N-based copolymers with improved adhesion, thermal stability, and permittivity. We discovered that a copolymer of tetravinyl-tetramethyl-cyclotetrasiloxane and Parylene-N has a permittivity of close to 2.1 and both the adhesion to SiQ2 and thermal stability are measurably improved compared to the homopolymer.

The development of materials with dielectric constant (K) less than SiO2 (K=3.9) is essential to meet the stringent speed, power dissipation and crosstalk requirements that are driving the low power integrated circuit (IC) paradigm. Both the low K dielectric and the processing methodology used for it should satisfy several important criteria before the technique can be accepted in future mainstream low power IC manufacturing. We had reported earlier a chemical vapor deposition (CVD) technique for the deposition of DuPont's Teflon amorphous fluoropolymer 1600 (bulk K=1.93) using the principle of direct liquid injection. The processing was carried out with and without an ultra violet (UV) light source in a computerized rapid isothermal processing (RIP) system.

Recently, we have extensively characterized the films and examined the suitability of our technique in light of some of the requirements of the future IC industry. Our results indicate that the processed films exceed several of the established dielectric performance standards outlined in recent roadmaps for sub 0.25 μm ICs. The film properties were improved when the UV source was used during processing. CVD processed films in general demonstrated significant improvements in terms of manufacturability, throughput, cost, and dielectric properties over the same films processed by alternate techniques.

One potential low dielectric constant material for ULSI multilevel interconnect applications is parylene AF-4, an organic polymer more formally known as Poly (α, α, α’, α’ - tetrafluoro-p-xylylene). In this study parylene AF-4 films were vapor-deposited on silicon wafers by pyrolytic decomposition of the cyclic dimer, cyclodi(α, α, α’, α’ - tetrafluoro-p-xylylene) using four different deposition conditions. Two different wafer temperatures and two different vaporizer temperatures were used, while the chamber pressure was kept constant. High vaporizer temperature and low wafer temperature give the highest deposition rates. It was found that the surface roughness of films of similar thickness showed a dependence on the deposition conditions. The films deposited at a low vaporizer temperature exhibit a smooth surface (RMS ∼ 4 nm) while those deposited at high vaporizer temperature have a rougher surface (RMS ∼ 16 nm). However, other properties of the films remained very similar. The FTIR spectra and refractive indices, both TE and TM, were measured for the films deposited using the four different deposition processes and showed no dependence on deposition conditions. These results indicate that the change in surface roughness is not due to a large difference in the chemical bonding among the films deposited using the four processes. Also, both weight loss and thickness loss of the films were measured after thermal cycling the films to 450°C and no significant differences were observed. This result indicates that the observed increase in surface roughness with increased vaporizer temperature cannot be related to a change in dimer incorporation in the films. Further experiments are planned to investigate the role of the initiation stage of the polymerization on film surface morphology.

Parylene-N thin films were characterized from the viewpoint of advanced VLSI intermetal dielectric applications. All films were deposited in a prototype production system that included a vacuum chamber, electrostatic cold chuck and a parylene vapor delivery system. Chuck temperatures as low as -30 °C were achieved. The deposition rate was found to be strongly dependent on wafer temperature, increasing dramatically as wafer temperature is reduced. Deposition rate was also strongly dependent on the parylene vapor flow rate and process pressure. These strong dependencies require that extreme care be taken to achieve production worthy repeatability.

A number of film properties were measured including; dielectric constant, refractive index, stress, adhesion, conformality, OH-content, metals-content and thermal stability.

Parylene polymers are vapor deposited and form semicrystalline films. The properties of these films vary with chemical structure, molecular weight, and morphology. The properties of parylene films deposited by changing the standard deposition process are evaluated and compared to control films. The thermomechanical properties of films produced by three modified processes, A, P, and PC, indicate the modified processes reduce the molecular weight. The films were also annealed to determine the stability of the film's properties during thermal cycling. These results also suggest that the modified films are lower molecular weight materials.

Previous work has demonstrated the potential of polytetrafluoroethylene (PTFE) thin films for ULSI applications. The films are deposited from PTFE nanoemulsions. They have an ultra-low dielectric constant of 1.7 to 2.0, a leakage current of less than 1.0 nA/cm2 @ 0.2 MV/cm and a dielectric strength of from 0.5 to 2.4 MV/cm. They are thermally stable (isothermal weight loss < 1.0 %/hr at 450 °C), uniform (thickness standard deviation < 2%), and have excellent gap-fill properties (viscosity of 1.55 cP and surface tension of 18 mN/m). The films are inert with respect to all known semiconductor process chemicals, yet they are easily etched in an oxygen plasma.

This paper discusses the processing technology that has been developed to process PTFE films with these properties. Specifically, it addresses two recent discoveries: 1) Good adhesion of spin-coated PTFE to SiO2 surfaces; and 2) high dielectric strength of PTFE thin films spin-coat deposited onto rigid substrates. The adhesion-promoting and thermal treatments necessary to produce these properties are detailed. Stud pull test results and test results from metal-insulator-metal (MIM) capacitor structures are given.

The fluorine doped TEOS films obtained using an inorganic gaseous dopant source (SiF4) and an organic liquid dopant source (TEFS) are described. The stability of fluorine in these films is strongly dependent on process conditions. The limit of stability for the most stable films is described. The gap fill capability of these films was found to depend strongly on the type of the fluorine precursor.

Polyamic amides or polyamic esters are alternative polyimides precursors exhibiting a better storage-stability than classical polyamic acids. Two original synthetic routes to these polymers were investigated through either diisoimides and diimidazolides in order to enhance stability and to obtain pure para catenation.

Polyimides prepared from oxydiphthalic anhydride and diamine precursors can be photosensitive. The thermal, mechanical, and dielectric properties of the polyimide films have been characterized with various techniques. The thermal decomposition temperature of the cured film is 520 °C, and the coefficient of thermal expansion is 20 × 10−6/°C. The polymer chemistry and processing conditions result in a low stress (<26 MPa) in the polyimide film as measured in situ during the curing and cooling cycles. Pads of 6 μm were patterned through the photosensitive polyimide at a sensitivity of 110 mJ/cm2 to i-line wavelength. The polyimide films exhibit anisotropy with an in-plane refractive index of 1.74 and an oul-of-plane index of 1.62 measured at 632.8 nm wavelength. This indicates a preferred orientation of polymer chains in the film plane. The estimated dielectric anisotropy should be considered a major factor for device design and optimization.

While fluorinated silicate glass (FSG) has been proposed for low k inter-metal dielectric (IMD) applications in a multi-level interconnect system either as the only IMD material, or as one of the materials for a multi-layer IMD system, thermal stability of the FSG film and its impact on device reliability remain a concern for this application. In this study, SIMS, SEM, and optical microscope analyses were carried out to evaluate the thermal stability of the FSG films and the possible reactions between FSG and metals. It was observed that at elevated temperatures fluorine tends to diffuse into an undoped oxide film rather than be desorbed. The data indicate that F diffuses 3.5 times faster in a silicon oxide film than in a silicon nitride film. Sub-half micron devices were processed with FSG as IMD layers. The devices were tested using an intensive thermal stability test methodology. A TiSi2 reaction with F which diffused from the FSG film was observed under optical microscopy. This reaction caused TiSi2 delamination. Electrical characterization of devices was performed before and after the thermal stability test. Although the device performance did not change greatly, the reaction certainly affects the long term device reliability (vide infra). Barrier materials were investigated to solve the F diffusion problem. With the proper diffusion barrier, the problem of the fluorine reaction with TiSi2 and subsequent metal blistering was eliminated.

Variations in stress and grain size of Ti- and TiN- capped Al thin films passivated by fluorinated silicon dioxide (SiOF) during repetitive thermal cycling are investigated. The amount of stress relaxation, elastic and plastic behavior of these thin film structures are compared. Ti and TiN cap layers strengthen the single Al film significantly while the presence of SiOF induces plastic deformation of metal layers. Less grain growth is associated with a dielectric passivated Al film. The penetration of fluorine into Al upon annealing can be reduced by a TiN barrier layer.

There is considerable interest in insulators with static dielectric constants lower than SiO2; an alloy system attracting recent attention is Si-O-F. Alloying of F atoms into plasma-deposited SiO2 films leads to major changes in the SiO2 bond-stretching and -bending infrared bands accounting for a significant fraction of the reduction in the dielectric constant. These changes are explained by F induced modifications of force constants and effective charges of the neighboring Si-O-Si groups.

The quality of TEOS fluorosilicate glass (FSG) films deposited on deep silicon trenches was investigated by etching the films with 100:1 HF. The etch rate of the top and sidewall surfaces was measured by SEM as a function of FSG fluorine content. The FSG wet etch rate was correlated to the refractive index, stress and fluorine content. The sidewalls were found to etch slower than the top surfaces, suggesting a lower fluorine content on the sidewalls. Additionally, the step coverage of TEOS oxide improved significantly as fluorine content was increased.

The adhesion of Al(Cu-Si) line structures on thin films of BPDA-PDA with different surface preconditioning were examined by measuring the deformation energy of the metal and interface. The properties of BPDA-PDA/Al(Cu-Si) were examined with atomic force microscopy (AFM). Although different sputtering treatments profoundly affect the adhesive properties, the sputtering does not appreciably change the topology of the BPDA-PDA. We also found evidence that even though the thickness of the interface can be very small (3–5 nm), the polymer/metal interface can greatly affect the deformation behavior of the entire system.

The effect of post plasma treatment on dielectric properties and reliability of fluorine doped silicon oxide (SiOF) films were investigated by measuring their C-V and I-V characteristics, XPS, AFM, and AES. The post plasma treatment of SiOF films was carried out in-situ at 300 °C in the deposition chamber. In this research, when the post plasma treatment time increased, we obtained the following results: (1) The etch rate of SiOF films decreased from 80Å/sec to 10Å/sec. (2) Surface roughness of the plasma treated SiOF films was increased due to the ion bombardment effect of the plasma. (3) The refractive index and relative dielectric constant increased from 1.391 to 1.461 and 3.14 to 3.9, respectively, due to the changes of surface chemistry by the post plasma treatment. (4) The leakage current density of SiOF films prepared by ECRCVD using SiF4 and O2 was less than 1 × 10−9A/cm2. (5) The breakdown field strength increased from 3.5 MV/cm to 8 MV/cm. (6) The thermal stability of the Cu/TiN/SiOF/Si system remained stable up to 600 °C.