Direct-write electron-beam systems

Future Direct-Write Electron Beam Systems... 

The two principal modes of operation of electron-beam exposure systems include the maskless direct-write electron-beam machines and the mask-based electron-beam machines. Direct-write electron-beam machines operate directly from design data and are capable of extremely high resolution. Mask-based electron-beam systems utilize masks in their imaging process. The implementation of electron-beam lithography in mix-and-match mode with optical lithography in a manufacturing environment has been demonstrated. 

Fig. 39. Schematic showing the basics of cell projection. The desired beam shape is selected by steering the electron beam through the appropriate pattern in the aperture plate. By using a rectangular aperture the system can operate like a conventional direct-write e-beam tool, so any shape of pattern can be...

In a typical direct write e-beam lithographic system, the resolution of a dense line-space array is often limited by the effect of electrons backscattered from the substrate. In these arrays, the backscattered electrons from one exposed line increase the net exposure density in an adjacent line. While this problem of non-uniform exposure can be corrected by varying the exposure dose within the pattern, this form of proximity correction requires sophisticated algorithms and extensive computer facilities. 

As already discussed, there is an important case where resolution is determined by fundamental limitations of the electron optical system and not by electron scattering. This occurs with the high current shaped electron beams used in high throughput direct-write tools. The Coulomb interaction between electrons in these columns displaces the electrons from their intended trajectories and blurs the edges of the spot. As discussed above in connection to throughput, this effect, which is related to the Boersch effect (45) forces a compromise between throughput and resolution. 

Focused ion beams can be used to expose resist, to write directly diffusion patterns into semiconductor substrates, and to repair masks. These techniques can potentially simplify semiconductor device production and perhaps reduce cost. Many of the technological challenges with ion beams are similar to those encountered with electron beams, but the development of ion sources and focusing/deflection systems are at a much earlier stage of development so application to manufacturing is several years away. 

Electron beam resists to be used in direct wafer writing for submicron devices need significant improvement in sensitivity, resolution and dry etching durability. Multilayer resist (MLR) systems are now regarded as the most important technology to perform practical submicron lithography for VLSI fabrication (1-3). Many advantages in MLR compared with one layer resists (1LR) are listed here ... 

H. Ito and E. Flores, Evaluation of onium salt cationic photoinitiators as novel dissolution inhibitor for novolac resin, J. Electrochem. Soc. 135,2322 (1988) H. Ito, Aqueous base developable deep UV resist systems based on novel monomeric and polymeric dissolution inhibitors, Proc. SPIE 920, 33 (1988). T. Aral, T. Sakamizu, K. Katoh, M. Hashimoto, and H. Shiraishi, A sensitive positive resist for 0.1 p,m electron beam direct writing hthography, J. Photopolym. Sci. Technol. 10, 625 (1997). 

In electron-beam direct-write lithography, the scanning electron beam of the exposure systems is focused to a small spot that is controlled [i.e., deflected and turned on and off (blanked)] by a computer as it is scanned across the surface of the resist film. Masks are not used in this exposure process. Two beam-forming approaches are employed. The first uses a Gausssian round beam. The second... 

The main advantage of NIL techniques, over direct-write techniques such as electron beam lithography, is that NIL can be used for rapid replication of nanoscale features on a wafer substrate. There are several variations of NIL, developed by different manufacturers of NIL systems. The following sections give a brief overview of some of the most important concepts of NIL. 

A precise positioning stage driven by friction with an ultrasonic motor provides a promising solution for an electron-beam direct-writing system for the next generation LSI, and has been realized by the optimum design of overall system using the concept described above. 

---