High aspect ratio feature

SupercriUcal Fluid DeposiUon (SFD) Metal films may be grown from precursors that are soluble in CO2. The SFD process yields copper films with fewer defects than those possible by using chemical vapor deposition, because increased precursor solubility removes mass-transfer hmitations and low surface tension favors penetration of high-aspect-ratio features [Blackburn et al.. Science, 294, 141-145 (2001)]. 

Conventional mtcrofabricated AFM tips are of limited use for investigating high aspect ratio features ( e. deep and narrow features), mainly because, without special treatment typical aspect ratios of such tips would be around 3 1 or lower. Thus, the width of such a tip at a certain height from the apex is much larger than that of the nanotubes of uniform thickness adhered to the tip. The nanotubes therefore would be more suitable for the analysis of deep and narrow structures than the commonly available tips. CNTs have been used as AFM tips and there appears to be every likelihood that extremely narrow structures can be probed.140 WS2 could be mounted on the ultrasharp Si... 

Surface-enhanced PBS films can be used in selective anisotropic reactive-ion etch processes to reproducibly delineate high aspect ratio features with submicron resolution. 

In addition to the reactor scale, which is measured in meters, vapor-phase mass transport effects can also be important in CVD at a much smaller scale, one measured in micrometers. This is often referred to as the feature scale . On this scale, the gas is generally in the transition or molecular flow regimes, rather than continuum flow. Mass transport on this scale plays an important role in the CVI processes discussed in Chapter 6. These phenomena are also important in CVD involving high-aspect ratio features, which can occur unintentionally in some growth morphologies and deliberately in microelectronics applications. 

In conclusion, the requirement to obtain a high aspect ratio features dictates a necessity to increase EF. As discussed in this section, the anisotropy of localized anodization depends on the process conditions, such as anodization voltage, electrolyte composition and temperature, the depth of porous-type anodization, the presence of alloying elements in Al, and the dimensions of features, which undergo porous-type anodization. As shown, voltage is the primary variable, which allows one to increase EF. At the same time, localized anodization of patterned Al substrates became isotropic as the depth of porous AI2O3 formation increases and the width of anodized features decreases. These trends have to be taken into account while utilizing porous-type anodization for EMM of Al substrates. 

Plating of high-aspect-ratio features is of key interest to micromachinists in general and in particular for those interested in LIGA (see below). Both electroless and electrodeposition can be used for this application. 

It must he mentioned that SC CO2 has been touted as the solvent of choice for potentially replacing a few, if not all, wet processes in the semiconductor lithography clean room of the future because of a number of inherent advantageous attributes. It is nonhazardous and inexpensive. It has high diffusivity (very comparable to that of a gas), which may aid in rapid effective dissolution. It has no surface tension since its liquid and vapor state are not simultaneously present, which may thus aid in mitigating pattern collapse issues of high aspect ratio features. Its solution properties can be tuned with minor adjustments of temperature and pressure. 

Microdevices fabrication for MEMS and other microengineering applications have been reported in Chapter 10. It presents a clear view on fabrication of microfeature of aluminum, copper, stainless steel, nickel, and titanium, etc., for MEMS. Some of the interesting topics included in this chapter are fabrication of high aspect ratio features for MEMS as well as micromachining of semiconductor by EMM. Here, EMM has successfully demonstrated its capabifity as an alternative technique for machining of microdevices with three-dimensional features of higher resolutions on metals as well as semiconductors. 

High aspect ratio features Hybrid tooling Microfiuidics Microinjection molding Micro... 

As mentioned above, materials processing varies strongly from material to material as well. There are other numerous types or dry and wet etchings that work for these different materials, each with its own unique characteristics. For example, reactive ion etches can create well-defined, high aspect ratio features with straight, smooth sidewalls in numerous materials but typically require much more handling and equipment. Wet etches are much simpler but less precise techniques that are compatible with... 

Nanostructures comprising various high aspect ratio features will be fabricated by electrochemical dissolution reactions controlled by crystallographic orientation, by masks, and/or photoelectrochemically by light. 

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