Commercial photoresists

Figuras 6 and 7 Mass spectra acquired from a commercial photoresist, using positive- and negative-ion detection, respectively.

Figure 19 shows the ultraviolet absorption spectrum of a typical diazonaphthoquinone and a common novolac resin. The naphthoquinone sensitizer has a strong absorbance at the 365 nm., 405 nm., and to a lesser extent the 436 nm. mercury emission lines. There are two diazonaphthoquinone isomers that are used in commercial photoresist formulations that are available at this time. The 5-arylsulfonates are by far the most commonly used. A spectrum of a representative of this class of materials is depicted in Figure 20. The 5-arylsulfonate materials are characterized by an absorbance maximum at approximately 400 nm. and a second, slightly stronger maximum at approximately 340 nm.

PE, RIE and IM resistances for an extensive list of commercial photoresists are included as well for comparison with the vinyl systems and amongst themselves. Although the exact com-osition of these systems is not public information, the generic type of base resin or polymer binder is generally known. In addition, the photoactive components are all known to be aromatic azides or azo-compounds. 

Table VII Commercial photoresist etch rate ratios.

SU-8 Brand of commercial photoresist from MicroChem, Newton, MA, USA... 

WitzgallG, Vrijen R, Yablonovitch E, Doan V, Schwartz B (1998) Single-shot two-photon exposure of commercial photoresist for the production of three-dimensional structures. Opt Lett 23 1745-1747... 

The molar extinction coefficient of the l-oxo-2-diazonaphtho-quinone-5-arylsulfonate (structure 3.2) sensitizers that are used to formulate most commercial photoresists is very low at 313 nm compared to that at 405 nm. 

AZ2400 is different from most other commercial positive photoresists in both formulation and response to mid-UV radiation. This resist is formulated with a resin that is relatively transparent in the mid-UV and l-oxo-2-diazonaphthoquinone-4-arylsulfonate (structure 3.3) rather than the 5-arylsulfonate (structure 3.2) that is commonly used in most commercial photoresists (24). 

A positive resist system can be of either two types. The classical diazoquinone system represents a photochemical rearrangement reaction which is the basis of commercial photoresists. Scissloning or degradation of a polymer chain by light or electrons Is a later example of solubility induced change. We will examine this change in detail. 

In this work, a quantitative evaluation method has been developed to measure photoresist sensitivity or speed (2,3) and process latitude (2,4) in order to compare positive photoresist performance under equivalent conditions. Performance data using this method will be reported and compared for an extensive group of first and second generation commercial photoresists. 

Photocyclization is a particularly valuable route to the formation of cyclic compounds. There is a wide variety of photocyclization reactions reported in the literature of organic photochemistry, but relatively few of these have been carried out in solid polymers. The earliest reports concern the photodimerization of cinnamic acid derivatives, leading to crosslinking in solid polymers. These polymers have important applications as commercial photoresists. The chemistry has been reviewed by Delzenne (46) and Williams (47). 

Figure 18 Examples of specific structures of PAGs that have been used in commercial photoresist formulations.

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