Bisazide, photolysis

Cyclized polyisoprene has been used as a photoresist by being sensitized with bisazides(1-3). Recently, H.Harada et al. have reported that a partially cyclized 1,2-polybutadiene showed good properties as a practical photoresist material in reproducing submicron patterns (U ). S.Shimazu et al, have studied the photochemical cleavage of 2,6-di(h -azidobenzal)cyclohexanone in a cyclized polyisoprene rubber matrix, and have reported that the principal photoreaction is the simultaneous cleavage of the both azido groups by absorption of a single photon with a U3% quantum yield(5 ). Their result does not support the biphotonic process in the photolysis of bisazide proposed by A.Reiser et al.(6 ). 

Miura and Kobayashi studied the photochemistry of 4,4-biphenyl bisazide. They concluded that photolysis of this diazide leads to extrusion of a single molecule of nitrogen with the formation of a singlet state species, X , with a lifetime of 19 ns. Miura and Kobayashi did not specify the nature of X. This species absorbs at 380 nm and its spectrum and lifetime are similar to our results with singlet para-biphenylnitrene. Therefore we conclude that X is singlet 4 -azido-4-biphenylnitrene. 

A comparative study of polystyrene (PS) with bis(perfluorophenyl) azides 1-2 and the corresponding non-fluorinated bisazides 3-4 as deep-UV resists is reported. Inclusion of as low as 1.2 wt-% of 1 in PS led to 70% retention of thickness after photolysis and development. PS containing 2.4 wt-% of 1 is > 100 times more sensitive as a deep-UV negative resist than PS itself. The presence of 1 in PS also increased the contrast of the resist. On a molar basis, 1 was about 10 times as effective as non-fluorinated bisazide 3 in cross-linking PS while 2 was about 6 times as effective as 4. PS containing 2.4 wt-% of 1 was found to have a deep-UV sensitivity of 5-10 mJ cm and resolution of about 0.5 /tm. 

Photolysis of 1 in clohexane gave bis-CH insertion product 5 (45%), mono-CH insertion product 6 (21%) and bis-aniline 7 (18). The isolation of bis-amine 5 appears to be the first instance in which a bisazide has been demonstrated photochemically to give a bis-CH insertion product. In contrast, photolysis of 3 under identical conditions gave no isolable product other than red tar. 

Figure 1. Effect of concentration on exposure characteristics for resists of PS-bis-PFPA 1, PS-bisazide 3 and PS itself. Resist films were exposed in a Rayonet photoreactor (254 nm) and developed in xylene for 30 sec then rinsed in isopropanol for 10 sec. The normalized film thickness was determined by IR at 2924 cm (CH absorption) before photolysis and after development.

---