A Research Of A High Precision Multi-channel Data Acquisition System Based On VME Bus

In recent years, with integrated circuits as the core, microelectronics technologyhas advanced rapidly and promoted lithography technology headed by opticalprojection lithography steadily. With the continuous improvement of the opticalprojection lithography resolution, depth of focus (DOF) has been shortenedaccordingly. The repeatability precision of the level adjusting system required in theoptical projection lithography is approximately1/10of the effective DOF, generallyabout ten nanometers. Therefore, the focusing sensitivity should be in nanometerscale. As a result, we need to increase the focusing precision to meet the requirementsof the focus adjusting system, and accordingly, put higher requirements for eachmodule of the focusing system.In the electric control system, the optical signals conveying the heightinformation of the chip are demodulated into8channel analog signals. To convert theanalog signals into digital ones which are more flexible and stable to process, adesirable data acquisition system is required. In this context, the universal dataacquisition module used in the focusing system now can’t meet the requirements ofnanoscale focusing system. This paper is aimed to develop a VME bus based highprecision multi-channel data acquisition system which can meet the requirements ofnanoscale focusing system.First, we briefly introduce the relevant theories and technical indicators of thedata acquisition system as well as VME bus, and propose the overall design scheme.Then possible interferences produced by other modules in the focusing system and theacquisition card itself are analyzed; corresponding methods are brought up to reducethe interferences in different modules. The design and implementation of everymodule are illustrated in details, and the control program used in the system is given.In addition, the hardware function module and software overall framework of thecontrol card is introduced. At last, the VME based high precision multi-channel dataacquisition system designed above is tested under the existing experimental condition.The preliminary results show that the technical indicators of the data acquisitionsystem as follows: the number of acquisition channel is8; the conversion precision is14bits; the input signal range is±5V; the sampling rate is adjustable within a range of30KHz; the magnification of the input signal is adjustable between1.18and4.83; data can be read and written by VME bus and interruption request is available. Inconclusion, the overall performance of this system meets the design requirements.