Interlayer dielectric

Another example of a cold-wall reactor is shown in Fig. 5.9. It uses a hot plate and a conveyor belt for continuous operation at atmospheric pressure. Preheating and cooling zones reduce the possibility of thermal shock. The system is used extensively for high-volume production of silicon-dioxide coatings for semiconductor passivation and interlayer dielectrics. 

Ali, I., Chemical-Mechanical Polishing of Interlayer Dielectric A Review," Solid State Technol., Vol. 34, 1994, pp. 63-70. 

An overview ofthe properties ofthe materials we are studying is presented in Table 18.11. The objective of this work was to find new approaches to the problem of generating new media with low dielectric constants and high thermal stabilities for use as interlayer dielectrics in microelectronic interconnection applications. We have been partially successful in this quest but there is still much more work to be done. The materials we have been able to deposit remain to be characterized in frill detail, which includes not only elucidating their molecular structure but also measuring the panoply of physical properties necessary for practical applications. 

Surface layers of silicon oxide are important in semiconductor device fabrication as interlayer dielectrics for capacitors, isolation of conducting layers, or as masking materials. However, anodic oxides, due to their relatively poor electrical properties, breakdown voltage, and leakage current, have not yet found much use in device technology, and cannot compete with thermal oxides obtained at high temperatures of 700 to 900 °C. 

Insulation Integrity. Insulation integrity is a function of an interlayer dielectric/passivant defined by specific electrical, mechanical and passivation properties. The D.C. electrical property of interest is the I-V characteristic which is used to deduce conductivity and breakdown field strength. The corresponding A.C. electrical property is dissipation factor. The pertinent mechanical and passivation properties are, respectively, pinhole density and performance rating as a diffusion barrier to Na" " and H2O. 

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... 

Because of the high functional values that polyimides can provide, a small-scale custom synthesis by users or toll producers is often economically viable despite high cost, especially for aerospace and microelectronic applications. For the majority of industrial applications, the yellow color generally associated with polyimides is quite acceptable. However, transparency or low absorbance is an essential requirement in some applications such as multilayer thermal insulation blankets for satellites and protective coatings for solar cells and other space components (93). For interlayer dielectric applications in semiconductor devices, polyimides having low and controlled thermal expansion coefficients are required to match those of substrate materials such as metals, ceramics, and semiconductors used in those devices (94). 

Polyimides, both photodefinable and nonphotodefinable, are coming into increased use. Applications include planarizing interlayer dielectrics on integrated circuits and for interconnects, passivation layers, thermal and mechanical stress buffers in packaging, alpha particle barriers on memory devices, and ion implantation (qv) and dry etching masks. 

Silicon dioxide films have been an essential factor in the manufacture of integrated circuits from the earliest days of the industry. They have been used as a final passivation film to protect against scratches and to getter mobile ion impurities (when doped with phosphorus). Another application has been as an interlayer dielectric between the gate polysilicon and the aluminum metal-ization. Initially, most such films were deposited in atmospheric pressure systems. In recent years, low pressure processes have assumed greater importance. We will begin by examining the atmospheric process. 

The low-temperature depositions described in the present section can be used for either interlayer dielectrics or final passivation films. Their primary disadvantage is one of film quality, because the process is susceptible to gas-phase nucleation and incorporation of particles into the film. 

Attention was then turned to a higher temperature, low-pressure process. Although such films would not be useful for final passivation, they could provide valuable interlayer dielectrics. At first. SiH4 with N20 was tried, where the reaction would proceed as follows ... 

For interlayer dielectric, another consequence of the addition of phosphorus and/or boron is the ability to "reflow" the glass at lower temperatures. Lowering processing temperatures is a continuing objective in CVD processing. 

The TEOS process just described has potential for use as an interlayer dielectric over metal layers that can withstand the high deposition temperature (i.e., doped polysilicon). If we want to cover aluminum, this process cannot be used. An alternative is to use a process where diacetoxyditertiarybutoxy-silane (DADBS)-(AcO)2Si(OtBu)2 will decompose at temperatures between 450° and 600°C.8... 

Finally, we will consider PECVD silicon oxynitrides, and their unique characteristics. When oxygen is added to a PECVD nitride film, there are indications that it may improve its crack resistance as a final passivation layer.13 Also, there may be advantages in terms of its electrical characteristics as an interlayer dielectric. Therefore, the nature of films grown when N20 is added to a SiH4, NH3 and He gas mixture in a high frequency (13.56 MHz), cold-wall, parallel-plate reactor have been studied. 

Policastro PP, Lupinski JH, Hernandez PK (1988) Siloxane polyimides for interlayer dielectric applications, Polymeric materials Science Engineering 59 209... 

For future high-speed microelectronic devices, copper interconnection with low dielectric constant (low-k) interlayer films is required to decrease RC (R interconnect resistance, C interlayer dielectric capacitance) delay. Recently, porous Si02 and silica-based films, developed for low-k films, have been extensively studied by positron annihilation spectroscopy [28], [29], [19]. Since Ps formation occurs with high probability, and the o-Ps annihilate via pick-off process in Si02-based materials, positron annihilation spectroscopy (especially PALS) gives useful information on the size of the pores. 

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