This paper reports the results of a study to integrate a metal-parylene interconnection system. The advantages and issues are highlighted. Fabrication steps for packaging geometries as well as proposed fabrication steps for VLSI applications are discussed. The relevant material properties for interconnection system design have been compiled.

As device geometries continue to scale down, a larger portion of the circuit delay is contributed by interconnects, and the majority of this delay is due to capacitive loading. The replacement of plasma-deposited SiO2 as an intermetal dielectric with an insulator of lower dielectric constant can provide performance improvement through the reduction of capacitance.

A commercially available polyimide, BiPhenylene DiAnhydride – Phenylene DiAmine, BPDA-PDA, with an out-of-plane dielectric constant 3.0, is evaluated by integration with AI(Cu) in a double level metal, BiCMOS 4MB SRAM device, with 0.5μm groundrules. Process challenges unique to integration of an organic rather than inorganic insulator are described and experimental features concerning process integration, particularly via etch, Al(Cu) deposition, adhesion and moisture management are presented.

Low dielectric constant films are being investigated as the interlayer dielectric (ILD) in a multilevel interconnection scheme for advanced ULSI circuits. In such applications they will be subjected to planarization processes using chemical-mechanical polishing (CMP), either directly during dielectric planarization or indirectly in the final stages of metal patterning using the Damascene process. In this paper we report the results of our initial investigations of the CMP of three different polymers, all with dielectric constant in the range of 2.3 – 2.7 and with different mechanical and chemical properties. The CMP was carried out using alumina as the abrasive in basic and acidic pH slurries. The effect of preannealing the polymer on the CMP behavior was also investigated

Fluorinated SiO2 films for use as interlayer dielectrics in ULSI multilevel interconnections are investigated. The interlayer dielectric film properties and their formation techniques have to meet the following requirements: (1) a low dielectric constant, (2) a high planarization capability, (3) a high capability for narrow gap filling, and (4) a low deposition temperature for low residual stress. To satisfy these requirements, three technologies have been investigated. They are: (i) a fluorinated SiO2 (SiOF) film by room temperature chemical vapor deposition (RTCVD-SiOF) using fluorotrialkoxysilane (FTAS) and pure water as gas sources, (ii) a room temperature liquid phase deposition (LPD) SiO2 film, and (iii) a fluorinated spin-on-glass (SOG) film by fluorotrialkoxysilane vapor treatment (FAST-SOG). The dielectric constant for SiO2 films can be reduced to 3.7 at 1 MHz by the RTCVD and LPD techniques. Although the FAST and RTCVD techniques cannot achieve full planarization, the LPD technique can achieve both global and local planarization because this technique has high capability for selective SiO2 film deposition. The RTCVD, FAST and LPD techniques have shown the possibility to reduce the film formation temperature to room temperature by catalytic reactions, resulting in low residual stress. Other properties of the RTCVD-SiOF, LPD-SiO2 and FAST-SOG films are good enough for the interlayer dielectric film application. The LPD-SiO2 film shows higher endurance properties to moisture than the RTCVD-SiOF and FAST-SOG films.

Fluorinated amorphous carbon films are proposed as low dielectric constant interlayer dielectrics for ULSI circuits. The films are deposited by plasma enhanced chemical vapor deposition with CH4, CF4 and C2F6 in a parallel-plate rf (13.56 MHz) reactor and a helicon wave reactor. In a parallel-plate reactor, the dielectric constant of the amorphous carbon films deposited with CH4 increases with increase in rf power. Addition of CF4 to CH4 reduces the dielectric constant to 2.1 and raises the deposition rate. However etching reaction occurs with high CF4/CH4 ratios. No film grows with only CF4. XPS measurement reveals that the F atoms are introduced into the amorphous carbon films. Helicon reactor has higher plasma density and is expected to achieve higher deposition rate for productive use. In this reactor, fluorinated amorphous carbon films without hydrogen content can be obtained with only CF4 and C2F6 gases. The growth rate of the films reaches 0.3 μ/min with C2F6 and 0.15 μ/min with CF4 at a source power of 2 kW and a gas flow rate of 100 sccm. With heating up to 300°C in a vacuum for 1 hour, the thickness of the films deposited with C2F6 does not shrink while that of films with CF4 shrinks.

Methyl siloxane spin-on-glass (SOG) is a conventional gap-filling material. In accordance with the requirement of low permittivity, many of major SOG suppliers are developing new types of methyl siloxane SOGs.

The most interesting property of these SOGs is their permittivity, which we measured by making stack structures of Al-0.5%Cu / TEOS CVD SiO2 / SOG / n+ Si. We also studied I-V characteristics, refractive indices, FT-IR spectra, stress, and moisture resistance.

All of the SOGs showed small stress and fair moisture resistance. Leakage currents were less than 2.5E-10 A/cm2 for bias voltages up to 5V. Permittivities ranged from 2.9 to 3.6. We observed a correlation between permittivity and FT-IR spectral features associated with Si-O-Si bonds. Reducing the number density of Si-O-Si bonds may be an effective way to lower the permittivity of this class of SOGs

Low density silica xerogels have many properties which suggest their use as a low dielectric constant material. Recent process improvements to control capillary pressure and strength by employing aging and pore chemistry modification, such that shrinkage is minimal during ambient pressure drying, have eliminated the need for supercritical drying. Although xerogels offer advantages for intermetal dielectric (IMD) applications because of their low dielectric constant (<2), high temperature limit, and compatibility with existing microelectronics precursors and processes, they suffer from unanswered questions. These include: 1) are all pores smaller than microelectronics features, 2) what are their mechanical properties (for processing and particle generation), and 3) what is their thermal stability. We have produced bulk xerogels under similar conditions to those used for films and studied the effect of density on the pore size distribution and bulk modulus.

Silica aerogels are highly porous solids having unique morphologies in which both the pores and particles have sizes less than the wavelength of visible light. This fine nanostructure modifies the normal transport mechanisms within aerogels and endows them with a variety of exceptional physical properties. For example, aerogels have the lowest measured thermal conductivity and dielectric constant for any solid material. The intrinsically low dielectric properties of silica aerogels are the direct result of the extremely high achievable porosities, which are controllable over a range from 75% to more than 99.8%, and which result in measured dielectric constants from 2.0 to less than 1.01. This paper discusses the synthesis of silica aerogels, processing them as thin films, and characterizing their dielectric properties. Existing data and other physical characteristics of bulk aerogels (e.g., thermal stablity, thermal expansion, moisture adsorption, modulus, dielectric strength, etc.), which are useful for evaluating them as potential dielectrics for microelectronics, are also given.

Although films of diamond-like carbon (DLC) and hexagonal boron nitride (h-BN) have shown low dielectric constants in the range of 3 to 4, these materials have been unsuitable for use as interconnect dielectrics due to poor thermal stability and environmental degradation. These deficiencies can be addressed by depositing DLC films free of hydrogen (a-tC) and depositing the cubic phase of BN (c-BN). The dielectric characteristics of hydrogen-free DLC and c-BN that have been deposited by pulsed-laser deposition (PLD) have been evaluated using metal-insulator-metal and metal-insulator-semiconductor structures. For comparison, the dielectric characteristics of h-BN deposited by electron cyclotron resonance (ECR) were also evaluated. Despite the superior thermal and environmental stability of the a-tC and c-BN films and the attractively low deposition thermal budget (room temperature deposition for a-tC films, 400°C for c-BN films), the films exhibit dielectric constants comparable to those of bulk diamond and bulk BN, ∼ 6. Furthermore, the a-tC and c-BN films exhibit high compressive stress in the GPa range which limits their usefulness only to those applications requiring a thin dielectric layer, e.g. diffusion barriers or encapsulants.

We demonstrated that the quality of siloxane spin-on glass (SOG) films, widely used as interlevel planarization dielectrics, is improved significantly by curing in argon plasma. The wet etch rate of SOG film decreases with increasing plasma treatment temperature or treatment time, and is much lower than that cured in a furnace. Long-time plasma treatment reduces the density of silanols (Si-OH) and methyl (−CH3) group, which act as adsorption sites of water. The results were compared with those obtained from the N2O (or H2 ) plasma treated SOG films. The modification of the SOG film by Ar plasma is related to the radiation damage and the reconstruction of the atomic structure during the plasma exposure. The role of metastable Ar (Ar*) appears to be very important to improve the SOG film; SOG film is more relaxed by the energy released from the conversion of Ar* to Ar.