Insulating Layers in Integrated Circuits

Layers of SiOi have several uses in the production of silicon ICs  

SiOi layers can be obtained by direct oxidation by one of the following reactions  

Dry oxidation is slow, but produces a uniform relatively defect-free layer that is electrically very reliable. Wet oxidation is more frequently used for masking operations because the growth rate is faster, however, the layers are not as uniform as those produced by dry oxidation. 

The oxide layer formed on the silicon surface is what is known as a protective oxide. The growth rate initially follows a linear rate law, i.e., the oxide thickness, x, increases linearly with time, t 

These values are close to the energy required to break the Si-Si bond, 1.83 eV. 

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Silicon Monoxide. SiO deposited by CVD and PVD methods to form dielectrics and insulating layers in integrated circuits, and as a protective coating. 

The proposed appUcatirms of aerogel are numerous and vary a great deal yet most remain uiu ealized. Commercial applications such as thermal window insulatirHi, acoustic insulation, optical coatings, capacitor electrodes, low dielectric constant layers in integrated circuits, piezoelectric transducers, and catalytic supports have all been proposed, but little in the way of actual use has resulted [1, 5-11]. However, sihca aerogel monohths have been used extensively in Cerenkov radiation detectors in high-energy physics experiments [12-16]. 

Deposition of Thin Films. Laser photochemical deposition has been extensively studied, especially with respect to fabrication of microelectronic stmctures (see Integrated circuits). This procedure could be used in integrated circuit fabrication for the direct generation of patterns. Laser-aided chemical vapor deposition, which can be used to deposit layers of semiconductors, metals, and insulators, could define the circuit features. The deposits can have dimensions in the micrometer regime and they can be produced in specific patterns. Laser chemical vapor deposition can use either of two approaches. 

The increasing importance of multilevel interconnection systems and surface passivation in integrated circuit fabrication has stimulated interest in polyimide films for application in silicon device processing both as multilevel insulators and overcoat layers. The ability of polyimide films to planarize stepped device geometries, as well as their thermal and chemical inertness have been previously reported, as have various physical and electrical parameters related to circuit stability and reliability in use (1, 3). This paper focuses on three aspects of the electrical conductivity of polyimide (PI) films prepared from Hitachi and DuPont resins, indicating implications of each conductivity component for device reliability. The three forms of polyimide conductivity considered here are bulk electronic ionic, associated with intentional sodium contamination and surface or interface conductance. 

Thin films (qv) of vitreous silica have been used extensively in semiconductor technology. These serve as insulating layers between conductor stripes and a semiconductor surface in integrated circuits, and as a surface passivation material in planar diodes, transistors, and injection lasers. They are also used for diffusion masking, as etchant surfaces, and for encapsulation and protection of completed electronic devices. Thin films serve an important function in multilayer conductor insulation technology where a variety of conducting paths are deposited in overlay patterns and insulating layers are required for separation. 

Polpmides have excellent thermal stability, solvent resistance, radiation resistance, wear resistance, hydrolytic stability, low dielectric constant, high mechanical properties, good chemical resistance and a low dielectric constant. Due to these superior properties, the application field of polyimide has generally been enlarged from printed circuit boards and electrical insulation layers in microelectronics to functional layers of humidity sensors, shielding layers for sensor surfaces and novel platforms for thermal sensor devices, temperature sensor arrays, micro-hotplates integrated into gas sensors and biosensors. 

Pig. 2. (a) The cell mount design of the integrated PV array of Pigure 1, which uses laminated conductive and insulating layers on top of an aluminium substrate in a printed circuit board-type panel (7). The array produces 20 kW at 20°C ambient and 850 W/m direct sunlight, and measures 155 m. The lens is a molded acryUc Presnel lens parquet mounted on the front of the array stmcture. The PV panel is mounted on the back of the array stmcture and is... 

Manufacture of Printed Wiring Boards. Printed wiring boards, or printed circuit boards, are usually thin flat panels than contain one or multiple layers of thin copper patterns that interconnect the various electronic components (e.g. integrated circuit chips, connectors, resistors) that are attached to the boards. These panels are present in almost every consumer electronic product and automobile sold today. The various photopolymer products used to manufacture the printed wiring boards include film resists, electroless plating resists (23), liquid resists, electrodeposited resists (24), solder masks (25), laser exposed photoresists (26), flexible photoimageable permanent coatings (27) and polyimide interlayer insulator films (28). Another new use of photopolymer chemistry is the selective formation of conductive patterns in polymers (29). 

Diffusion Barriers. Diffusion barriers are used in the production of various components in the electronic industry. For example, electrochemically deposited nickel is used as a barrier layer between gold and copper in electronic connectors and solder interconnections. In these applications the product is a trilayer of composition Cu/Ni/Au. In another example, Ni and Co are considered as diffusion barriers and cladding materials in the production of integrated circuits and multichip electronic packaging. In this case the barrier metal (BM), Co or Ni, is the diffusion barrier between conductor and insulator (i.e., Cu and insulator), and the product trilayer is of composition Cu/BM/insulator. The common couple in these applications is the Cu/BM bilayer (BM, the diffusion barrier metal Co, Ni, or Ni-Co alloy). 

Since the invention of integrated circuits (ICs), polyimides as heat-resistant organic polymers have been applied to insulation materials in electronics devices such as flexible printed circuit boards (FPCs), interlayer dielectrics, buffer coatings, and tape automated bonding (TAB). A polyimide thin layer is easily... 

Photo-resist technology is widely used for imaging processes in such applications in electronics. If it is wished to produce a metallic pattern of connections between many electronic components (resistors, capacitors, integrated circuits, etc.), this can be done by the selective etching of a thin copper plate deposited on an insulating base. The copper layer is protected by a resist which is a polymer, deposited in such a way that it prevents the attack of the metal by an etching solution which will solubilize only the unprotected, exposed copper (Figure 6.8). 

To fabricate the integrated circuit (IC), layers with various electrical properties must be introduced into or deposited onto the substrate. These layers may consist of insulating, semiconducting, and conducting films. The construction of the layers in only the desired areas relies on a series of patterning steps which is briefly illustrated in Figure 1. Light sensitive... 

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