Sensitivity lithographically useful

This imposes a limitation on the sensitivity of the resist, i.e., it is necessary to design a resist that will react sufficiently to to produce a lithographically useful, three-dimensional relief image. Now let us consider the four subsystems and their limitations. 

We have also demonstrated other lithographic uses for polysilanes as nonimageable O2-RIE barrier layers (9), as short wavelength contrast enhancing materials (26) and more recently as sensitive, positive e-beam resists (36). 

The lithographically useful lifetime of fused silica is dependent on many parameters, including (i) lens design as it relates to peak laser fluence, polarization and temperature sensitivity, and phase error tolerance, and (ii) laser parameters such as pulse duration (higher peak fluences must he applied in shorter pulses). 

Fig. 7.2). In practice, exposure to doses sufficient to result in no loss of resist thickness produces some undesirable exposure of unexposed regions due to interference or scattering effects. If this dose exceeds DJj, which is often the case, a residue is left effectively broadening the image. It is usually avoided by exposing at a lower dose, e.g. D , where accurate reproduction of linewidths is obtained. This is the lithographically useful sensitivity which is usually quoted for the resist material. 

The sensitivity of positive resists is similarly determined by measurement of resist thickness with dose (Fig. 7.4). In this case the lithographically useful sensitivity is the dose at which the resist is just removed after development, D°, without affecting the thickness of unexposed resist. The contrast is also determined as before as the gradient of the linear portion of the curve... 

Haley, N. F. Corbiere, S. L. Radiation-Sensitive Composition Containing a Resole Resin and a Novolac Resin and Use Thereof in Lithographic Printing Plates. U.S. Patent 5,372,907, December 13, 1994. 

Lithographic Characteristics. Based on the potential of crosslinker 3 to show high sensitivity and contrast and wide process latitude, it was of interest to evaluate its lithographic capability, using crosslinker 1 as the standard for comparison. Crosslinkers 1 and 3 (equal weight) were each incorporated into otherwise identical experimental AHR resist formulations. E-beam exposures were performed so that differences in DUV absorbance characteristics of the crosslinkers could be ignored. The e-beam sensitivities of the resists containing crosslinkers 1 and 3 were 6.2 and 4.2 (lC/cm2,... 

As we mentioned before, G(s) is a structure dependent constant that describes the number of scissions per unit absorbed dose and in that sense can be compared to a photochemical quantum efficiency. The G(s) of a radiation-sensitive polymer is a figure of merit that can be used in comparing one material with another. There is a very high correlation between G(s) values to gamma radiation (the radiation most commonly used for determining G(s)) and high sensitivity for lithographic materials used in either electron beam, ion beam or x-ray exposure. 

Polyphosphinoboranes are of interest with respect to their potentially useful physical properties such as flame-retardant behaviour and an ability to function as precursors to BP-based ceramics. In addition, the electron-beam sensitivity of some polyphosphinoboranes has been demonstrated. This allows their use as lithographic resists for patterning applications when coated as thin films on substrates such as silicon (Figure 9.11). ... 

As a general rule, the sensitivity of conventional electron beam resists is not sufficient for economic throughput in an x-ray lithographic system. This is particularly true of positive electron resists such as PMMA, the most widely used x-ray resist for experimental purposes, whose sensitivity of >500 mJ/cm2 is some 100 times too slow for practical application. Even PBS only shows a sensitivity of 94 mJ/cm2 to PdLa x-rays. Consequently, the major research effort has concentrated on negative resists because of their higher inherent sensitivity. 

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