Chemical amplification photoresists

Name of 248 nm positive chemical amplification photoresists Chemical amplification of resist lines... 

Electron spectroscopy for chemical analysis Environmentally stable chemical amplification photoresist Extreme UV... 

A new type of copolymer resist named ESCAP (environmentally stable chemical amplification photoresist) has recently been reported from IBM [163], which is based on a random copolymer of 4-hydroxystyrene with tert-butyl acrylate (TBA) (Fig. 37), which is converted to a copolymer of the hydroxystyrene with acrylic acid through photochemically-induced acid-catalyzed deprotection. The copolymer can be readily synthesized by direct radical copolymerization of 4-hydroxystyrene with tert-butyl acrylate or alternatively by radical copolymerization of 4-acetoxystyrene with the acrylate followed by selective hydrolysis of the acetate group with ammonium hydroxide. The copolymerization behavior as a function of conversion has been simulated for the both systems based on experimentally determined monomer reactivity ratios (Table 1) [164]. In comparison with the above-mentioned partially protected PHOST systems, this copolymer does not undergo thermal deprotection up to 180 °C. Furthermore, as mentioned earlier, the conversion of the terf-butyl ester to carboxylic acid provides an extremely fast dissolution rate in the exposed regions and a large... 

This paper deals with the application of the tautomerism of uracO to a chemical amplification photoresist. Pofyethers containing 2,4-dialkoi pyrimidine units (3) were prepared. These polymers were found to be very sensitive to an acid and to be applicable to diemical amplification photoresists (Scheme 3). 

The latest addition to this list of dry developing resist materials is a contribution from IBM s San Jose Research Laboratory (66-67) that evolved from efforts to design positive-tone resist materials that incorporate chemical amplification. These efforts were stimulated by the fact that the quantum yield of typical diazoquinones of the sort used in the formulation of positive photoresists is 0.2 to 0.3 thus, three or four photons are required to transform a single molecule of sensitizer. This places a fundamental limit on the photo-sensitivity of such systems. 

Note 2 The term chemical amplification is commonly used in photoresist lithography employing a photo-acid generator or photo-base generator. 

When chemical amplification type photoresists are stored after exposure, they are influenced in several minutes by basic organic substances contained in the environment in even a slight amount of less than about 10 ppb, and the desired resist patterns sometimes cannot be obtained. Therefore, containers used for storing and carrying these contents are required to exclude the outside contaminating substances. In addition, the containers themselves are required not to generate contamination substances. 

Ester derivatives of 4-hydroxyl polystyrene, (III), prepared by Suetsugu [3] were effective as chemical amplification type positive photoresists. 

Thus, these new copolymers form the basis of a new, deep UV, thermally stable photoresist. This resist combines the high Tg and thermal stability of the styrene-N-(p-hydroxyphenyl)maleimide copolymer and the sensitivity of the chemical amplification design concept. 

Figure 4.28. Molecular structures and photoinduced reactions of common photoresists. Shown (top) is the positive tone resist containing the active diazonapthoquinone (DNQ) chromophore group. Chemical amplification (CAM) reactions are illustrated in (i)-(iii). Reaction (i) represents photoinduced acid generation step (ii) is an acid-catalyzed deprotection mechanism (positive tone resist) and step (iii) is an acid-catalyzed crosslinking mechanism (negative tone resist).

Postexposure bake of the wafer. A postexposure bake (PEB) improves contrast of the photoresist before its development. The PEB process causes three effects 1) diffusion of the PAC 2) solvent evaporation and 3) thermally induced chemical reactions. In general, the dissolution rate of a resist decreases as a function of a PEB temperature. PEB becomes more important for the photoresists with a chemical amplification (CA) feature. The photoresists need the PEB to complete chemical reactions initiated by exposure. 

The diazido-ort/io-naphthoquinone/novolac (DNQ/ novolac) photoresists have been the workhorse for the semiconductor industry for over 30 years and still continue to be the most widely used photoresists today. ° They may be utilized with different exposure wavelength technologies I-line (365 nm), G-line (436 nm), and even 248 nm. Although productivity requirements for the technology with 248 nm exposure have demanded the transfer to photoresists with a chemical amplification, the DNQ-novolac resists still remain to be the most widely used and constantly finding new areas of implementation. The modern state-of-the-art in the microdevices technology gives an opportunity to use the DNQ-novolac resists to print features as small as 0.25 In addition, these photoresists in the form... 

In 1979, Frechet and Willson put forward a very productive idea of a chemical amplification that was used in the development of a new generation of photoresists.They decided to use a photoresist comprising of a photochemical acid generator (PAG) and a polymer that was able to switch from hydrophobic to hydrophilic in the course of acid catalyzed hydrolysis. The PAG reacts with light to produce an acid catalyst. During a subsequent postexposure bake, the catalyst diffuses and reacts with the polymer component, causing many reaction events in the polymer and recovers the acid catalyst. The acid molecules catalyze the deprotection reaction and provide a prerequisite for chemical amplification. The number of the reaction events initiated by single quantum absorption has been estimated to be of order of 100. ... 

The following reaction scheme can present a simplified mechanism occurring in the photoresists with chemical amplification chemistry. 

The chemical amplification idea appeared when it was necessary to develop photoresist material having high sensitivity, high resolution, and good plasma etch resistance. It was desirable primarily when the 248 nm exposure became the requirement of the industry. And the result of implementation of the idea was very good. Chemical amplification as a basic ideology of the photoresist creation partly worked at the 193 nm millstone. ... 

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. 

This system, denoted as Environmentally Stable Chemical Amplification Positive Photoresist, ESCAP, has become the standard 248 nm resist in device manufacture by leading chip makers. It is capable of printing features with a density of 125 nm [29]. 

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... 

SCHEME 57.1. Chemical amplification in a positive-tone photoresist. 

A decrease in exposure wavelength translates to new types of photoresists that will be stable upon contact with higher energy radiation. Whereas the DNQ photoresist system is effective in the MUV range, photoresists that feature chemical amplification (CAM) moieties are used exclusively for DUV and shorter wavelengths.The enhancement of quantum efficiency and sensitivity results... 

This study has demonstrated that excellent photoresist materials incorporating chemical amplification can be obtained using polymers operating on the basis of acetal chemistry. A variety of acetal groups are available for designing novel... 

Recently chemical amplification type photoresists have been developed. In the present paper, we described a novel analytic method of photoadd generation. This method is very simple and useful for investigation of photoadd generators. 

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