Thin-film deposition dielectric constants

The CCS approach is well matched to the synthesis part of the problem of the identification of new thin-film high dielectric constant materials for embedded DRAM applications. As noted above, low-temperature deposition is essential and the CCS approach provides in situ mixing at low temperatures. Samples are obtained in thin-film form and can be made in thicknesses that are similar to those that will actually be used. 

There is also growing iaterest ia thin-film dielectric capacitors. For example, through the use of processiag techniques such as sol—gel solution deposition, thin (--- 0.25 fim) ceramic layers having dielectric constants ranging from 500 to 2000 ia the PZT, Pb(Zr,Ti)03, and PMN—PT, Pb(Mn2 3Nb2 3)03-PbTi03, compositional families respectively, have been prepared (3). 

The main objective of the work to be described here is to design and synthesize new organic dielectric materials, and to develop new techniques to deposit these materials as thin, thermally stable films with very low dielectric constants, for use as ILDs. New dielectric materials must not only possess proper electrical, thermal, and mechanical properties but should also minimize or eliminate the use of solvents in this era of concern for environmental pollution. 

Even though some ferroelectric materials, especially the relaxor ferroelectrics, have an extremely large dielectric constant, which is a very desirable property for the dielectric layer of capacitors in ULSI DRAMS, the usually large dielectric loss prevents the materials from being used in the DRAMS. Furthermore, the quite large number of component cations of the relaxor ferroelectric materials makes it almost impossible to deposit thin films using chemical vapor deposition (CVD) which is believed to be the method of choice for mass production of the devices. 

Polynapthalenes are in general, rigid rodlike low molecular weight aromatic polymers and are insoluble in most common solvents. Thin films of polynapthalene deposited by CVD are microcrystalline as deposited, and show a low dielectric constant (e = 2.4), with high dielectric breakdown strength (3 MV/cm), along with excellent thermal stability (dissociation temperature 570°C). CVD studies have so far been done primarily in view of their low dielectric constants, for use as intermetallic dielectrics in ULSI interconnect applications. 

In the relentless quest for ever faster computer circuitry, the dielectric constant of the insulating layers between conductors on the chip is becoming a major issue. This constant should be as small as possible while the mechanical properties of the dielectric material must withstand the subsequent processing steps and ensure the integrity of the computer microprocessor. Nanoscale zeolite crystals, particularly pure silica zeolites, have been proposed as candidates for thin films with low dielectric constant (low k). As an example, suspensions of nanoscale crystals of the pure zeolite silicalite-1 (MFI-typc) were used for spin-on deposition of thin dielectric layers.[101] The as-deposited films were subsequently calcined at 450 °C in order to remove organic molecules and to consolidate the films. The authors report low dielectric constants (although the adsorption of humidity must be controlled) and satisfactory mechanical properties of their films. 

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