Novolac-based resist, characteristics

Figure 3 shows the sensitivity curves for SPP (solid lines) compared with that of a novolac-based resist (dashed line). From these curves, we obtained the maximum clearing dose (Dq), the dose for 50% thickness remaining (D50), and lithographic contrast (7-value). These resist characteristics are summarized in Table I. 

Novolac- or phenolic resin-based resists usually show no pattern deformation induced by swelling during development in aqueous alkaline solution. Examples of such resists are naphtho-quinonediazide/novolac positive photoresists, novolac-based positive electron-beam resist (NPR) (1), and azide/phenolic negative deep-UV resist (MRS) (2). Iwayanagi et al.(2) reported that the development of MRS proceeds in the same manner as the etching process. This resist, consisting of a deep-UV sensitive azide and phenolic resis matrix, is also sensitive to electron-beams. This paper deals with the development mechanism of non-swelling MRS and its electron-beam exposure characteristics. 

This system has been reported to show good photosensitivity (—100 mJ/cm2 in the 230-300 nm range) with extremely high contrast. Values of 7 > 5 were observed, compared to 2 for conventional systems. Chandross et al. believe the high contrast stems from the unusual dissolution characteristics of the resist in that the basic "developer" appears only to "prime" the irradiated regions for subsequent development in the aqueous rinse. The resist formulation is essentially aliphatic in nature and would be expected to be less stable to dry etching environments than the aromatic-based novolac resin materials. 

Other characteristics of DNQ/novolac resists that have contributed to their lasting success in the semiconductor industry include their high etch resistance and the fact that they can be developed in environmentally benign aqueous base developers. In addition, the cyclized rubber/bis-azide negative tone resists did not image well at the Hg g-line, the exposure wavelength of the earliest commercially available wafer steppers, the introduction of which effectively brought about the complete and wholesale conversion of the IC industry to novolac resists from the cyclized rubber/bis-azide. ... 

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