Negative working resist

In a negative working resist the monomer is first polymerized over the entire copper surface, then the protective polymer layer is irradiated through the mask. In the irradiated areas the polymer is degraded into smaller units and becomes soluble it can then be removed by treatment with a suitable solvent and the etching bath will attack this exposed copper. 

The surface photo absorption for contrast enhancement (SPACE) process has been recently reported for use with a negative-working electron-beam resist (42). By addition of a controlled UV-flood exposure step, enhancements in both contrast and sensitivity of MRS RD2000N resist, a negative working resist composed of poly(p-hydroxystyrene) and 3,3 diazido-diphenylsulfone, have been obtained. However, its application is iimited to negative working resists. 

Ito and C.G. Willson, Chemical amplification in the design of dry developing resist materials, Polym. Eng. Sci. 23, 1012 (1983) H. Ito, C.G. Willson, and J.M.J. Frechet, Positive and negative working resist compositions with acid generating photoinitiator and pol3mier with acid labile groups pendant from polymer backbone, U.S. Patent No. 4,491,628 (1985). 

Most negative-working resist systems are based on the fact that the dissolution rate of a polymer decreases as the molecular weight increases, and the polymer ultimately becomes insoluble in any solvent as a crosslinked network is formed. 

An electron beam is of much shorter wavelength than the radiation used in standard microlithography and, therefore, provides greater resolution possibilities. For resist exposure a beam of electrons can be used whose position is controlled by a computer-driven beam deflector, thus obviating the need for a mask. Both positive- and negative-working resists are used for electron beam lithography. 

As stated above, PVSE 1) is soluble in cold water 2) has a high Si-content and 3) it is anticipated to be a negative working resist through the crosslinking reaction of side chains by certain stimuli such as UV and EB, because PVSE possesses two reactive double bonds in each repeating unit. Thus, the resist... 

Both negative and positive working photoresists have been formulated with epoxy resins [11, 17]. The example in Fig. 2.9(a) is mixed with a polyamine resin to give a cataphoretic, negative-working resist [17], while that in Fig. 2.9(b) is reacted with a DNQ-sulphonyl chloride to give an anaphoretic, positive-working resist [11]. 

The sensitivity of positive-working photoresists is similarly determined (as for negative-working resists section 2.4.4b) by measurement of resist thickness with varying exposure energy [21]. 

Some negative-working resists contain an inhibitor compound, usually based on hydroquinone, that prevents spurious thermal crosslinking of the monomer on standing, thereby increase shelf life. 

Ito, H., Willson, C.G., and Frechet, J.M.J. (1985) Positive and Negative Working Resist Compositions with Add Generating Photoinitiator and Polymer with Acid Labile Groups Pendant from Polymer Backbone. US Patent 4,491,628. 

Takahashi, A. Shirakawa, H. Adegawa, Y. Chemically-amplified negative-working resist compositions for processing with electron beam or x-ray. Jpn. Kokai Tokkyo Koho JP 2003005355, 2003. 

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