New development strategies for high aspect ratio microstructures

Abstract

In the first step of the LIGA process a resist layer, typically PMMA (polymethylmethacrylate), is pattered by deep X-ray lithography. The exposed parts are subsequently dissolved by an organic developer. The quality and the achievable height of the microstructure is decisively determined by the development process. In order to increase the aspect ratio and maintain the quality of the microstructures the parameters influencing the development process were investigated. In the case of dip development and ultrasound development a strong dependency of the development rate on the temperature, dose value and depth of deposition has been noticed. The development rate increases with increasing dose value and temperature and decreases with increasing depth of deposition. In case of dip development the development course can be described by a phenomenological equation which considers the three mentioned parameters. In the case of ultrasound further parameters have to be taken into account: the geometry and the dimensions of the strucutres.

Development of a sonovoltammetric cell for mass transport investigations in the LIGA-process under megasonic agitation

“…The megasonic supported development of LIGA microstructures was first suggested and investigated by Zanghellini et al [2,5]. It was shown that the megasonic agitation increases the development rate and that the development rate depends on both the lateral form of the structures and the acoustical intensity.…”

“…How sensitive are the effects to probe location with respect to the megasonic source? Why do the same kind of structures on a single substrate show considerable deviations in the developed depth [5]? What benefits can megasonic agitation bring for electroforming?…”

Visualization of the development process in deep X-ray lithography

“…Another method, using a needle to measure the removal rate of the exposed material, does not allow classifying the removed gel-layer thickness, additionally the method does not provide measurements of smaller microstructures then the needle diameter which was 30 mm in Refs. [9,10].…”

Fabricating HARMS by using megasonic assisted electroforming

“…Acoustic agitation offers a promising approach to enhance the mass transport rates within HARMS (Zanghellini et al 1998). Previous research has shown that ultrasonic agitation may change a diffusion controlled electrodeposition process into a charge controlled one (Hyde et al 2002).…”