Within the microelectronics industry, there is an ongoing trend toward miniaturization coupled with higher performance. The scaling of transitors toward smaller dimensions, higher speeds, and lower power has resulted in an urgent need for low dielectric constant interlevel insulators. Low dielectric constant interlevel dielectrics have already been identified as being critical to the realization of high performance integrated circuits in the SLA Roadmap. Thus, there exists a need in the microelectronics industry for a thermally stable, noncorrosive low dielectric constant polymer with good solvent resistance, high glass transition temperature, good mechanical performance and good adhesive properties, particularly to copper. In addition, the desired dielectric material should be capable of being processed in environmentally friendly solvents, and the final thermal and electrical performance should not be affected by manufacturing or post environmental conditions. High glass transition temperature polynorbornenes are being developed which provide many of these desired features. This polymer family is produced via a new transition metal catalyzed polymerization. Attributes which make polynorbornene particularly attractive in microelectronics include: (i) excellent thermal performance, (ii) adhesion to conductors without the use of adhesion promoters or barrier layers, (iii) very low moisture absorption (< 0.1 wt %), and (iv) low dielectric constant (2.2 – 2.6). Side groups which have been added to the polynorbornene backbone improve adhesion, dielectric properties and mechanical properties.

A novel polymer has been developed for use as a thin film dielectric in the interconnect structure of high density integrated circuits. The coating is applied to the substrate as an oligomeric solution, SiLK*, using conventional spin coating equipment and produces highly uniform films after curing at 400 °C to 450 °C. The oligomeric solution, with a viscosity of ca. 30 cPs, is readily handled on standard thin film coating equipment. Polymerization does not require a catalyst. There is no water evolved during the polymerization. The resulting polymer network is an aromatic hydrocarbon with an isotropie structure and contains no fluorine.

The properties of the cured films are designed to permit integration with current ILD processes. In particular, the rate of weight-loss during isothermal exposures at 450 °C is ca. 0.7 wt.%/hour. The dielectric constant of cured SiLK has been measured at 2.65. The refractive index in both the in-plane and out-of-plane directions is 1.63. The flow characteristics of SiLK lead to broad topographic planarization and permit the filling of gaps at least as narrow as 0.1 μm. The glass transition temperature for the fully cured film is greater than 490 °C. The coefficient of thermal expansivity is 66 ppm/°C below the glass transition temperature. The stress in fully cured films on Si wafers is ca. 60 MPa at room temperature. The fracture toughness measured on thin films is 0.62 MPa m ½. Thin coatings absorb less than 0.25 wt.% water when exposed to 80% relative humidity at room temperature.

Fluorinated amorphous carbon (a-C:F) films sandwiched between layers of SiO2 have been proposed as an interlayer dielectric (ILD) structure in order to enhance resistance to oxygen plasma. This study describes adhesion failure mechanisms for the sandwiched fluorinated amorphous carbon film (a-C:F) structure during oxygen plasma annealing. We have found 3 failure modes: 1) capping SiO2 layer peels off, 2) thickness reduction of a-C:F by decomposition, and 3) etching phenomena at the interface between SiO2 and a-C:F by CFx outgassing from a-C:F. The outgassed CFx radicals were stored at the interfaces and the etching of SiO2 occurred during the subsequent 150°C oxygen plasma resist removal process. Thermal decomposition of a-C:F ILD sandwiched between layers of SiO2 was performed to determine the outgassed species, as well as the thickness reduction of a-C:F.

Low dielectric constant materials (k < 3.0) have the advantage that higher performance IC devices may be manufactured with minimal increases in chip size. The reduced capacitance given by these materials permits shrinking spacing between metal lines to below 0.25 μm and the ability to decrease the number of levels of metal in a device. The technologies being considered for low k applications are CVD or spin-on of inorganic or organic polymeric materials. Traditional spin-on silicates or siloxanes have been used as planarizing dielectrics during the last 15 years and usually have k > 3.0.

Amorphous carbon films grown with fluorohydrocarbons can be grown to have dielectric constant values around 2.0. The behavior of these films when subjected to thermal excursion is studied. We have investigated material deposited in an ECR plasma, and find that the F:H ratio of the gas mixture is a good guide to material properties. Films deposited at 5°C were placed in a vacuum chamber at 400°C as long as 60 minutes. The film thickness, dielectric constant, and infrared absorption spectrum change with the F:H ratio of the incoming gas and thermal cycling. It was found that the dielectric constant and loss tangent decrease upon heating and that there is an apparent increase in C=C groups. As expected, as the F:H ratio increases, the dielectric constant and thermal stability decrease. Good thermal stability is shown for F:H ratios of 1.5, which result in films with a dielectric constant of ∼2.4 after heating.

Cure is a significant process during back end of the line fabrication of integrated circuits with hydrogen silsesquioxane since it affects structure and properties of the spin on dielectric material. Reported herein is the effect of soak temperature, time, and oxygen concentration process parameters on structure and properties of hydrogen silsesquioxane. Results of the study emphasize the importance of an inert environment during the baseline recommended cure conditions of 400 °C for one hour in order to avoid oxidation and formation of polar silanol or water species. A 350 °C cure temperature is more robust to oxidation providing similar or improved properties. Shorter cure times result in similar structure and properties as the baseline cure which suggests that lower temperature and/or shorter cure time may provide value worth investigating by integrated circuit manufacturers.

SOG etchback was studied using Applied Materials' 200mm MxP+ etch chamber on Allied Signal's SOG (spin-on-glass) T11 and low κ SOP (spin-on-polymer) 418 together with liner films of PE-oxide and oxynitride for IMD (inter-metal dielectric) planarization. Excellent chamber performance and wide process window were demonstrated. Etch selectivities between various SOG and liner films are tunable in a wide range allowing optimization of IMD planarization.

There are several activities in the development of low dielectric constant materials, including fluorlnation of SiO2, low-k organic polymers, and porous materials. No one material satisfies all the requirements for multilevel interconnections, which include low dielectric constant, high mechanical strength, good dimensional stability, good high temperature stability, easy processing, and low H2O absorption and outgassing. In this research, a new material system has been studied. This process-controlled low-k material can have dielectric constant as low as 2.0 with good thermal stability. It can provide low viscosity for reflow processing to achieve excellent planarization and gap filling. Low moisture uptake and high mechanical strength can be achieved. Most interesting is, it can be made to be photosensitive at deep-UV range, which provides the possibility of eliminating many chemicals and complicated processes in photolithography. Process cost can be expected to drop significantly. Damascene and dual damascene processes were proposed using this new low-k material, which can be much simpler compared to the traditional process.

XPS studies of Cu(I)hfac(COD)adsorbed on clean and alumina-modified Teflon-AF surfaces show that on the clean polymer surface, Cu(0) formation occurs between 300 K and 600 K in UHV. The corresponding reduction is hindered by the presence of an alumina adlayer. In addition, the Cu Auger kinetic energies indicate the formation of nanoparticles on the alumina surface at both 300 K and 600 K. Annealing from 300 K to 600 K results in a ∼4 eV shift of the Cu(2p) transitions to higher binding energies. These facts indicate that the Cu precursor reacts with the alumina surface and results in limited mobility and hindered Cu(I) to Cu(0) reduction on the modified polymer surface.

The influence of fluorine desorption from SiOF films deposited by biased ECR-CVD was studied. It was found that desorbed F atoms from the SiOF film react with Ti suicide film resulting in forming SiF4 gas. The evolution of SiF4 gas caused the peel-off of the films.

Interactions between fluorinated polyimide and aluminum under different thermal treatment conditions have been investigated using transmission electron microscopy (TEM) and x-ray diffractometry (XRD) techniques over a wide temperature range. Our results suggest that the oxygen from the dielectric materials may result in the oxidation of the underlying aluminum either on the surface or along the grain boundary. This work implies that processing conditions, such as curing temperature and time, may play critical roles in affecting the performance of polymeric dielectric materials.

Copper films with a small amount of an alloy element (1 wt % Ti) were metallized on polyimide. Plasma pre-treatment of the polyimide surface and post-metallization annealing were used to modify the interface. Interfaces and metal film layers were investigated; a drastic increase in adhesion strength, the suppression of Cu diffusion into polyimide, and the improvement of (111) texture were found. Composition analysis data taken from the interface indicated the accretion of nitrogen at the interface. The formation of Ti-related chemical bonds, suggested by X-ray photoelectron spectroscopy, can explain the above-mentioned experimental results.

As microelectronic device dimensions decrease and functionality density increases, a change in interconnect materials, both conductors and insulators must change from currently used materials. To this end, we are actively in search of low dielectric constant materials that can be integrated into integrated circuit production. The greatest limiting factor in materials qualification are the stringent IC processing conditions (thermal stability, resistance to chemical/mechanical treatments). Current specifications for back-end-of-the-line (BEOL) thin film insulators call for materials with dielectric constants of 3.0–3.5 and turn of the century CMOS devices may require materials with dielectric constants approaching 2.0. While there are a number of possible candidates for current uses, the list of usable materials with dielectric constants <3.0 is very limited. Future low K candidates being examined include fluorinated polyimides and porous materials.

The dielectric constants of silica aerogels are among the lowest measured for any solid material. The silica aerogels also exhibit low thermal expansion and are thermally stable to temperatures exceeding 500°C. However, due to the open porosity and large surface areas for aerogels, their dielectric constants are strongly affected by moisture and temperature. This paper presents data for the dielectric constants of silica aerogels as a function of moisture content at 25 °C, and as a function of temperature, for temperatures in the range from 25 °C to 450°C. Dielectric constant data are also given for silica aerogels that are heat treated in dry nitrogen at 500°C, then cooled to 25°C for measurements in dry air. All measurements are made on bulk aerogel spheres at 22GHz microwave frequency, using a cavity perturbation method. The results of the dependence found here for bulk materials can be inferred to apply also to thin films of silica aerogels having similar nano-structures and densities.

Hybrid organic-inorganic xerogel films were deposited as porous thin films by spinning the precursor sol on silicon substrates. Films of various compositions were prepared using combinations of the following precursors: methyltrimethoxysilane, dimethoxydimethylsilane and tetramethoxysilane (TMOS). The hybrid films exhibited excellent gap-filling capabilities (0.45 micron trenches). Thermal desorption experiments indicate that heating to ∼130 C removes moisture and volatile organic constituents present in the as-cast film. Curing was found to increase the adhesion between the xerogel and the silicon substrate. Moisture was found to be responsible for an increase in the dielectric constant. That is, in ambient, the dielectric constant for a cured film was found to be 4.4; but in a dry atmosphere, it decreased to 2.5. Current-voltage measurements show the cured hybrid film possesses a breakdown field of 3.4 MV/cm.

This paper presents the results of development, characterization and integration screening of low dielectric constant (low k) fluorinated polyimides for interlayer dielectric applications. Evolution of these materials has progressed with the intent of improving fundamental thin film properties, such as thermal stress behavior, modulus, CTE, and dielectric constant. Further refinements to fluorinated polyimides have been to improve their process compatibility and integration characteristics, primarily in the area of deep sub-micron gap filling. The avenues taken to attain these objectives will be illustrated.

Subsequent integration of low k fluorinated polyimides has been achieved for a completed single-level metal BEOL test vehicle to highlight the impacts of the film's adhesion, mechanical and thermomechanical properties. In addition, the completed fluorinated polyimide single-level metal structures have been used to characterize electrical performance in contrast to single-level metal structures with TEOS dielectric. Intralevel capacitance and leakage current have been measured with dual comb and serpentine structures. Modeling has been applied to verify dielectric constant in submicron geometries from the capacitance measurements.

This paper presents a study of the effects of electron beam (e-beam) exposure on the chemical and physical properties of FLARE™ 1.0X, a non-fluorinated member of the FLARE™ family of poly(arylene ether) dielectric coatings. Spin-coated films of this poly(arylene ether) were cured by large-area e-beam exposure, as well as by conventional thermal processing. Neither swelling nor dissolution was observed for the e-beam cured films after immersion in N-methylpyrrolidone (NMP) at 90 °C for 1 hour. The glass transition temperature (Tg) for films cured with a low e-beam dose is slightly higher than, or nearly the same as, the (Tg) for thermally-cured films (∼ 270 °C). However, the Tg for films cured with a high e-beam dose exceeds 400 °C. Dielectric constants of e-beam cured films and thermally cured films are nearly the same. FTIR spectra of FLARE™ films obtained before and after e-beam exposure suggest that e-beam curing does not induce any significant change in the chemical structure. Increased solvent resistance, higher Tg, and low dielectric constant are properties that make this e-beam cured poly(arylene ether) film an excellent candidate for interlevel dielectric integration processes.

Fluorinated polyimide can potentially replace TEOS as an interlevel dielectric in future ULSI interconnect technologies because its lower dielectric constant offers reduced crosstalk, signal propagation delay, and dynamic power dissipation. One issue associated with polyimides is the anisotropy in dielectric constant, where the smaller out-of-plane dielectric constant, typically measured using parallel-plate capacitors, can misleadingly exaggerate the advantage in reducing crosstalk. In this paper, we present a novel electrical technique to estimate the in-plane dielectric constant of DuPont FPI-136M fluorinated polyimide without requiring dielectric gapfill.

A blanket FPI-136M film is deposited over interdigitated inlaid Al(0.5%Cu) structures and the crosstalk capacitance is measured. Identical inlaid structures with air and TEOS passivations are also measured for capacitance calibration. Differences in measured capacitances reflect electric fields fringing in the various passivation dielectrics above the inlaid metal. With the known dielectric constants of air and TEOS, the effective dielectric constant of FPI-136M is interpolated to be 2.8. Interconnect simulations confirm that the effective dielectric constant extraction technique is valid and accurate provided that the passivation layer is sufficiently thick to contain the fringing fields.

To estimate the in-plane dielectric constant, we use simulations to determine the combination of in-plane and out-of-plane dielectric constants that is equivalent to the extracted effective dielectric constant. With an out-of-plane dielectric constant of 2.6, the in-plane dielectric constant of FPI-136M is estimated to be 3.0. This technique is applicable to other dieletrics.

New methodologies are being developed in our laboratory that allow measurements of the Young's modulus (E) and thermal expansion coefficient (TEC) for materials that cannot be prepared as free standing films. The first employs a bending beam measurement of stress versus temperature. We measure the thermal stress of a given film on two substrates, Si and GaAs. The use of two substrates allows the determination of both E and TEC. A TEOS film is used to demonstrate the technique. Another technique is a variation of the stress-strain measurement of E. The brittle material of interest is coated onto a polymer substrate, and the composite film is elongated to obtain the stress-strain curve of the composite film. Subtraction of the polymer substrate contribution to this curve yields the stress-strain behavior of the brittle film and allows calculation of E.

The in-plane dielectric constants of potential interlayer dielectrics (ILD) are determined from the interline capacitance between metal lines passivated with the material. We have developed a finite difference simulation to account for the fringe capacitance, and it allows the extraction of the in-plane dielectric constant from the measured capacitance. The method was used to measure the anisotropies in two polymer ILDs. A flexible chain polymer showed the same anisotropy in both a blanket film and on patterned lines, but a rigid rod-like polymer was found to be much less anisotropic on the patterned lines relative to the blanket film. This result indicates that the molecular orientation of the film is different on the patterned lines.

Metalized polypropylene film used in high energy density capacitors has been mechanically characterized to determine its elastic constants. The out of plane coefficient of thermal expansion (CTE) of the orthotropic film is 10 times as large as the smaller in plane CTE. The out of plane modulus is twice as large compared to one of the in plane moduli. The effect of interfacial pressure on the dielectric breakdown is also studied for the same film. It is observed that the dielectric strength of the film decreases at first and then increases above 4 MPa of compressive stress.