Resist polymer photoresist

In general, the photoresists exhibit greater dry-process resistance than the vinyl polymers of Table II. The greater dry-etch resistances of photoresists is attributed to the aromatic nature of the crosslinking agents, photoactive components, and novolac resins (positive photoresists only). In addition, the... 

Figure 11.25 PEB sensitivity curves for different acrylate and alicyclic/acrylate hybrid resist polymer platforms used in ArF lithography. The target CD was 120 nm L/S at 1 2 duty cycle. [Reproduced from R. Dammel, "Practical photoresist processing, SPIE Short Course No. SC616 (2005).]...

Figure 11.26 PEB stability of a conventional DUV 248-nm resist based on poly (4-hydroxystyrene-co-tert-butylcarbonyloxy styrene) versus ESCAP based on poly(4-hyd-roxystryene-co-tert-butyl acrylate). Note that the acid generated in the conventional DUV resist is trifluoromethane sulfonic acid (a very strong, small, volatile acid), while that of the ESCAP resist is camphor sulfonic acid (a very weak, bulky, nonvolatile acid). While the conventional DUV resist polymer is nonannealing, that of the ESCAP is an annealing polymer. [Reproduced from R. Dammel, Practical photoresist processing, SPIE Short Course No. SC616 (2005).]...

The next sequence calls for the coating of a thin layer of a hydrophiUc polymer from an appropriate solvent on top of the photoresist. The polymeric HOL must have a lower glass transition temperature (7g) than the photoresist polymer it must be able to diffuse into the photoresist polymer on baking and it must be phase compatible with the photoresist polymer. Suitable hydrophilic polymers include, but are not limited to, polymers and copolymers of fluoroalkyl methacrylic acid, fluoroalkyl acrylic acid, etc. Surfactants may be used to improve the wettability of the HOL over the resist polymer layer. 

The last step calls for the development of the HOL polymer/photoresist film stack in an aqueous basic solvent such as 0.26 N tetramethylammonium hydroxide. This will dissolve and wash away the exposed part of the resist, comprising the carboxylic acid moieties. The preferential diffusion of the HOL into the exposed area of the photoresist results in deprotection of the photoresist polymer at the edge of the unexposed features, leading to their dissolution. This is the basis of the CD reduction, improved process window, and exposure latitude, and smoother sidewall and line edge profile of photoresist features processed with HOL relative to the features processed without HOL. ... 

In this chapter, attention is focused on a number of polymers that are either themselves characterized by special properties or are modified for special uses. These include high-temperature and fire-resistant polymers, electroactive polymers, polymer electrolytes, liquid crystal polymers (LCPs), polymers in photoresist applications, ionic polymers, and polymers as reagent carriers and catalyst supports. 

Reactive Ion (PLASMA) Etch Resistance of Photoresist Polymers. 976... 

REACTIVE ION (PLASMA) ETCH RESISTANCE OF PHOTORESIST POLYMERS... 

For instance, polymers containing dimethylmaleimide pendant groups can be cross-linked by UV light with the formation of cyclobutadiene bridges, through the known 2 -h 2 photodimerization mechanism. These polymers have nothing to do with heat-resistant polymers they have been developed and studied because of their potential as photoresists. 

However, developments in the MEMS industry, which often relies on deep etching of silicon to fabricate micro-machine structures, require thicker resist layers and alternative polymer photoresists. 

Laser ablation of polymers has been known since 1982 [8, 19]. Many aspects of polymer ablation and laser processing, in general, have been described by Bauerle [20]. More recently Lippert and Dickinson [21] reviewed in detail the chemical and spectroscopic aspects of polymer ablation and new directions. Many types of polymers can be laser machined, the most common ones being PI, PMMA, polyethylene (PE), polycarbonate (PC), poly(ethylene terephthalate) (PET) and poly-etheretherketone (PEEK). Other polymers include polytretrafluoroethylene (PTFE), S-U8 resist, other photoresists and acrylics. 

To obtain a pre-formatted master, a polymer photoresist is spin-coated onto a glass disc, and is rotated with high precision under an argon-ion laser that is modulated with the information. The resist is then developed and coated with a thin layer of silver, and a nickel master is grown by electroplating. When the master is split away from the polymer, it contains a perfect replica of the pre-format information. 

Any discussion of the wide variety of advanced photoresist systems in use today would be incomplete without first discussing the early workhorse materials for the semiconductor industry. Recall that Figure 2 shows the progression of resist technologies that have heen associated with production of various feature sizes over the history of the semiconductor industry. A discussion of these early materials nicely motivates hoth many of the advances in resist polymer science and technology that have occurred over the last several decades and some of the problems yet to he addressed. 

Figure 37 Illustration of the concept of the RLS trade-off (i.e., resolution ine edge roughness-sensitivity trade-off) that occurs in conventional chemically amplified photoresist designs/formulations. Foragiven resist design (i.e., essentially foragiven resist polymer), one can typically reformulate the resist to achieve better properties in two of the three important performance metrics (i.e., R, L, or S) at the expense of worse performance in the third metric. Mew polymer designs or entirely new photoresist schemes are needed to improve aii three performance metrics simultaneously.

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

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