Metal nitrides, thin films

Homoleptic amido species M(NR2)s have been used as precursors for chemical vapor deposition of metal-nitride thin films. For example, Ta(NMe2)s and NH3 afforded Ta3N5 thin films with low carbon contamination at temperatures between 200 °C and 400 °C.85... 

A small number of MIV amido complexes have been prepared, usually by metathesis reactions from synthons such as MCl4(thf)2. The homoleptic amido species M(NMe2)4 have been examined as precursors of metal nitride thin films.85,477... 

Kim H (2003) Atomic layer deposition of metal and nitride thin films. Current research efforts and applications for semiconductor device processing. Journal of Vacuum Science Technology B 21(6), 2231-2261... 

These metal compounds can be made by high temperature (>100°C) reactions such as that of NH3 with the metal or metal oxide, or by lower temperature routes where metal halides are heated with Li3N or Na3Nn the latter method has been used for Ti, Cr, Mn, Hf, Y, and Sm nitrides. Thin films of nitrides can be made by chemical vapor deposition12 using amido compounds such as Ti(NMe2)4 and NH3 at 150-450°C at 1 atm. 

Bulk-micromachined membranes are usually formed from dielectric materials like silicon oxide or silicon nitride combined with additional materials for example, in pressure sensors, silicon is used to increase the membrane thickness to the required values and in thermal sensors, platinum or other metals are needed for the sensing elements. The overall stress state of the membranes has to be controlled well to prevent buckhng (under high compressive stress) or fracture (under high tensile stress). With proper processing control, silicon oxide and silicon nitride thin films meet this requirement, making them ideal candidates for membrane-type devices. 

The complex nature of the bonding structure in transition metal nitrides incorporates a mixture of covalent, metallic and ionic components [126]. The nature on this bonding leads to high hardness, chemical inertness and, good electrical conductivity of these mixed nitride thin films. In what follows, we describe the surface chemical alteration of both a control and oxidized Ti—Al—N films (i.e., two different types of deposition room temperature (A) and liquid N2 temperature (B)), by measuring the chemical shifts in the Ti (2p), Al (2p), O (Is) and N (Is) XPS spectra. 

Vanadium nitride thin film with the thickness of 400 nm was fabricated via the dc magnetron sputtering method from metallic vanadium target on glass substrate (61). 

The number of oxides is large since most metallic elements form stable compounds with oxygen, either as single or mixed oxides. However, the CVD of many of these materials has yet to be investigated and generally this area of CVD has lagged behind the CVD of other ceramic materials, such as metals, carbides, or nitrides. The CVD of oxides has been slower to develop than other thin-film processes, particularly in optical applications where evaporation. 

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

Several patents dealing with the use of volatile metal amidinate complexes in MOCVD or ALD processes have appeared in the literature.The use of volatile amidinato complexes of Al, Ga, and In in the chemical vapor deposition of the respective nitrides has been reported. For example, [PhC(NPh)2]2GaMe was prepared in 68% yield from GaMes and N,N -diphenylbenzamidine in toluene. Various samples of this and related complexes could be heated to 600 °C in N2 to give GaN. A series of homoleptic metal amidinates of the general type [MIRCfNROilnl (R = Me, Bu R = Pr, BuO has been prepared for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. The types of products are summarized in Scheme 226. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. 

A cross-sectional schematic of a monolithic gas sensor system featuring a microhotplate is shown in Fig. 2.2. Its fabrication relies on an industrial CMOS-process with subsequent micromachining steps. Diverse thin-film layers, which can be used for electrical insulation and passivation, are available in the CMOS-process. They are denoted dielectric layers and include several silicon-oxide layers such as the thermal field oxide, the contact oxide and the intermetal oxide as well as a silicon-nitride layer that serves as passivation. All these materials exhibit a characteristically low thermal conductivity, so that a membrane, which consists of only the dielectric layers, provides excellent thermal insulation between the bulk-silicon chip and a heated area. The heated area features a resistive heater, a temperature sensor, and the electrodes that contact the deposited sensitive metal oxide. An additional temperature sensor is integrated close to the circuitry on the bulk chip to monitor the overall chip temperature. The membrane is released by etching away the silicon underneath the dielectric layers. Depending on the micromachining procedure, it is possible to leave a silicon island underneath the heated area. Such an island can serve as a heat spreader and also mechanically stabihzes the membrane. The fabrication process will be explained in more detail in Chap 4. 

The rapid developments in the microelectronics industry over the last three decades have motivated extensive studies in thin-film semiconductor materials and their implementation in electronic and optoelectronic devices. Semiconductor devices are made by depositing thin single-crystal layers of semiconductor material on the surface of single-crystal substrates. For instance, a common method of manufacturing an MOS (metal-oxide semiconductor) transistor involves the steps of forming a silicon nitride film on a central portion of a P-type silicon substrate. When the film and substrate lattice parameters differ by more than a trivial amount (1 to 2%), the mismatch can be accommodated by elastic strain in the layer as it grows. This is the basis of strained layer heteroepitaxy. 

Thin films of carbides and nitrides of Group 6 metals were synthesized by reaction of a metal film with a reactive gas at high temperature and by reactive sputtering. The phases obtained depended on the experimental conditions. High temperatures metastable phases (/i-WC, v and 6-MoC]. ) were obtained by reactive sputter deposition of films. The carbon concentration in such films depended on the temperature of the substrate and on the pressure. In some cases ordered sublattices of carbon and nitrogen were observed and epitaxial relationships between the deposit and the substrate were studied. 

During the last years, a great number of studies have focused on transition metal carbides and nitrides because of their numerous technological applications. Thin films are particularly interesting in integrated circuits,1 in decorative coatings,2 and as hard surface layers in cutting tools.3... 

Carbide or nitride films were also made by reacting metal films deposited by thermal evaporation or d.c. sputtering on MgO or Si02 with a flow of reactive gas at high temperature. The reactive gas was a CH4/H2 mixture or pure NH3. The reaction time was typically 2-4 h. As it is known that many phases of the metals can exist (bcc Cr, fee Cr, bee Mo, fee Mo, bcc W, fee W,. . . ), we will only present in this chapter the results where the precursor is the normal phase (the bcc metal). The conditions to prepare thin films of metals in this form have been described earlier.10... 

The rapid development of solid state physics and technology during the last fifteen years has resulted in intensive studies of the application of plasma to thin film preparation and crystal growth The subjects included the use of the well known sputtering technique, chemical vapour deposition ( CVD ) of the solid in the plasma, as well as the direct oxidation and nitridation of solid surfaces by the plasma. The latter process, called plasma anodization 10, has found application in the preparation of thin oxide films of metals and semiconductors. One interesting use of this technique is the fabrication of complementary MOS devices11. Thin films of oxides, nitrides and organic polymers can also be prepared by plasma CVD. 

The studied coats based on titanium have partly semiconductor and partly metallic properties. The concentration of the free carriers is around 1019c j 3 i.e. greatly (three orders) less than in metal, but also 3-4 orders more than in semiconductors. The Fermi level in titanium nitride is located in the minimum of the state density formed by intersection of titanium d-zone and p-zone of nitrogen [5] (Fig. 8). Therefore such coats are offered as the most perspective thin-film defensive covering. 

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