Influence of development parameters on electron resist contrast

A 3D micro/nano structuring is finding more and more applications in different fields of since at last time. One of the 3D micro/nano structuring method is e-beam lithography. Measurement of electron resist characteristics especially contrast is very important for 3D structure fabrication. For this purposes the new express method for contrast determination was developed. This work is devoted to application of the method to investigation of contrast dependence on development conditions. It is based on an expression for resist development velocity: nu = nu 0 (D/D 0 ) gamma where v is development rate of the electron resist exposed with dose D, nu 0 is the development rate of the electron resist exposed with dose D 0 (resist sensitivity), and gamma is a contrast. The main feature of the method is the specially designed 3D test structure "dose wedge" in detail described. Three different profiles can, generally, be revealed after the development of the exposed "dose wedge". As shown, when gamma is higher than the real resist contrast gamma exp the profile is concave, when gamma < gamma exp the profile is convex, and when gamma and gamma exp are equal the profile is plane. Therefore, when gamma = gamma exp the change in the residual resist thickness is linear. The real test structures consist of several dose wedges. The article shows the results of the test structure development of a PMMA 950 K. resist exposed by a JEOL 840 A under NanoMaker hardware/software system control at 25 kV. The exposure data were designed using the software part of the NanoMaker. When the residual resist thickness grows linearly, the distance between neighboring intensity minima or maxima is constant. In the case gamma > gamma exp , the distance decreases with a thickness increment and, vice versa, if gamma < gamma exp the distance between minima or maxima increases with a thickness increment. For the test structure, the value of the resist contrast is 7. The considered method is similar to approach developed for measurements of proximity function parameters. The main advantage of the method in comparison with others is it speed (design, exposure, development and observation take typically 30 minutes). So this method gives possibility to investigate resist contrast as function of different lithography parameters for acceptable time. The results of the investigations can help to find ways for resist contrast manipulating. As example of the method application the contrast of the PMMA 950