New chemistries for atomic and molecular layer deposition and their applications

The deposition of thin films is an essential step in the fabrication of many consumer products, from the complex computer processor to the simple potato chip bag. Atomic layer deposition (ALD) is a method to deposit thin films with atomic control of the layer thickness. ALD films have good coverage and grow conformally on high aspect ratio structures. Due to their desirable properties, ALD films have gained in popularity and are now the thin films of choice for many applications. Consequently there is an increased demand to expand the database of materials that can be deposited by ALD and to integrate these films in applications. This thesis investigates both the deposition of two new materials by ALD, and the development of two new ALD applications.Molybdenum ALD is demonstrated by fluorosilane elimination chemistry using MoF6 and Si2H6 reactants. A variety of in situ and ex situ techniques are used to decipher the growth mechanism and film properties of this ALD system. According to quartz crystal microbalance (QCM) and Auger electron spectroscopy (AES) Mo ALD nucleates very rapidly on Al2O 3 surfaces, reaching a linear growth regime after only 4-5 ALD cycles. In the linear region Mo ALD has a very large growth rate and shows ideal ALD behavior for temperatures between 90 - 150 °C. Depending on the dosing rate of Si2H6 precursor, Mo ALD films can be grown without impurities or with 16 at % Si impurities, based on Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS) investigations. Varying temperature, precursor dose, and purge parameters does not have an effect on the amount of Si impurities. Fourier transformed infrared analysis (FTIR) reveals that MoFx species are reduced to metallic Mo during the Si2H6 dose. Glancing incidence x-ray diffraction (GIXRD) indicates that Mo ALD films were nanocrystalline. Due to their rapid nucleation rate, Mo ALD films could serve as adhesion layers for other metal ALD systems on oxide surfaces.Polymeric materials can be deposited by a new form of ALD known as molecular layer deposition (MLD). The growth behavior of a hybrid organic-inorganic MLD film using a three-step ABC sequence is investigated. This new system employs trimethyaluminum (TMA), as the inorganic precursor, and ethanolamine (EA) and maleic anhydride (MA), as the organic precursors. The choice of organic precursor to circumvent some of the problems that plague traditional MLD systems is discussed. The ABC MLD reaches a very large linear growth rate that has a strong dependence on the TMA dose and purge conditions. In situ QCM experiments reveal that the diffusion of the TMA in and out of the ABC film as it is forming plays an important role in the ABC growth mechanism. X-ray reflectivity (XRR) shows that despite their large growth rate, ABC films are very smooth, comparable to Al2O3 films grown by ALD. ABC films are stable in air, decreasing in thickness only by 5% in the first 3 days after growth. However, discrepancies between in situ and ex situ measured growth rates suggest that ABC films might suffer a very rapid initial degradation in air. The TMA diffusion hypothesis was corroborated by a good fit of the experimental data to fickian diffusion numerical modeling. The robust growth and smooth interfaces suggest that ABC films might be useful as flexible layers in multilayer barrier structures and as sacrificial layers in nanofabrication.The potential use of MLD films as sacrificial layers is one of the ALD applications that is addressed in detail. Due to their aluminum content hybrid MLD films cannot be dry etched with oxygen plasma because a protective Al 2O3 is formed at the surface. However, the MLD ABC film can be removed controllably by acidic solutions and is used as a sacrificial layer in a doubly-supported bridge nanostructure. The other application investigated here is the deposition by ALD of films with a lateral thickness gradient. High density materials, such as Mo ALD, and low density materials, such as ABC MLD, produce x-ray Bragg mirrors when are deposited as thin films in an alternating fashion to form a periodic structure. However, a lateral gradient of these multilayers is needed to fabricate x-ray focusing optics. The deposition of laterally graded layers by ALD is studied and optimized, with gradients of various desired pitches ranging from 119 to 444 A / in. being accomplished.