Based on chemical amplification

As discussed previously, an optional postexposure, predevelopment bake can reduce problems with the standing-wave effect in DNQ-novolac positive resists. However, such a postexposure bake step is indispensable in the image reversal of positive resists (37-41) and certain resists based on chemical amplification of a photogenerated catalyst (64-67, 77, 78). For both types of resists, the chemistry that differentiates between exposed and unexposed areas does not occur solely during irradiation. Instead, differentiation occurs predominantly during a subsequent bake. Therefore, to obtain acceptable CD control in these systems, the bake conditions must be carefully optimized and monitored. 

MacDonald, S.A. Schlosser, H. Ito, H. Clecak, N. Willson, C.G. Plasma developable photoresist systems based on chemical amplification. Chem. Mater. 1991, 3, 435-442. 

Kaimoto, K. Nozaki, S. Takechi, andN. Abe, Alicyclic polymer for ArF and KrF excimer resist based on chemical amplification, Proc. SPIE 1672, 66 (1992). 

How the balance between the above-named requirements are struck in each of the major advanced resist-processing schemes in use today is discussed below, along with the advantages and drawbacks of each technique. In particular, we discuss the material basis of the resolution limit issues of resists, especially as they concern those based on chemical amplification systems, since these constitute the majority of resists in use in advanced lithographic processing today. 

Advanced photoresists, such as 193 and 248 nm photoresists, are based on chemical amplification concept [7,8]. These chemically amplified photoresists generally consist of a base polymer, a photo-sensitive compound called photoacid generator (PAG), and sometimes a cross-linking... 

Major advances in radiation sensitivity have been achieved by applying the concept of chemical amplification to photolithography [252-254]. Chemical amplification is related to a cascade of chemical reactions that are initiated by a single photon. In fact, strategies based on chemical amplification have played a key role in the development of novel resist systems, as will be outlined in the following subsection. It is to be noted, that the chemical amplification concept has served the semiconductor industry as a workhorse for the past few decades. 

Figure 11.6 Ultrasensitive bioassays of proteins and nucleic acids based on the amplification features of carbon-nanotube carriers and modified electrodes (Reproduced with permission from [51 ]. Copyright 2004, American Chemical Society)...

Dry-Film Resists Based on Radical Photopolymerization. Photoinitiated polymerization (PIP) is widely practiced ia bulk systems, but special measures must be taken to apply the chemistry ia Hthographic appHcations. The attractive aspect of PIP is that each initiator species produced by photolysis launches a cascade of chemical events, effectively forming multiple chemical bonds for each photon absorbed. The gain that results constitutes a form of "chemical amplification" analogous to that observed ia silver hahde photography, and illustrates a path for achieving very high photosensitivities. 

Synthetic oligonucleotides are very important tools in the study and manipulation of DNA, including such techniques as site-directed mutagenesis and DNA amplification by the polymerase chain reaction. The techniques for chemical synthesis of oligonucleotides are highly developed. Very efficient automated methodologies based on solid phase synthesis are used extensively in fields that depend on the availability of defined DNA sequences.52... 

Chemical heat pump uses chemical reaction for thermal energy storage and conversion. The heat pump operation is based on reaction equilibrium relationship, and has two operation modes. Figure 221 shows equilibrium relationship of chemical heat pump cycle for Mg0/H20 system at (a) heat amplification and cooling mode and (b) heat transformation mode [26], Figure 222 shows... 

A number of new resist materials which provide very high sensitivities have been developed in recent years [1-3]. In general, these systems owe their high sensitivity to the achievement of chemical amplification, a process which ensures that each photoevent is used in a multiplicative fashion to generate a cascade of successive reactions. Examples of such systems include the electron-beam induced [4] ringopening polymerization of oxacyclobutanes, the acid-catalyzed thermolysis of polymer side-chains [5-6] or the acid-catalyzed thermolytic fragmentation of polymer main-chains [7], Other important examples of the chemical amplification process are found in resist systems based on the free-radical photocrosslinking of acrylated polyols [8]. 

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